Well, I read a beautiful list of tips on Hoowee's Anime Fruitloops site and a smallish section at The Inuyasha Technical Resource, and got a similar idea to put on mine. Mostly, this was spawned by some things I noticed while reading fanfics at Fanfiction.net, and I probably suffer some of these problems in my writing. I thought it might be helpful to have a list of these on my own site. They may not apply to you, but then again they may. Only you really know. Apply them to your writing if you will, but you aren't required to. These are simply tips that I hope will help people write better, or at least more tolerable, fanfiction. And since I have a tendency to hang out in the Inuyasha section of Fanfiction.net, some of these will apply specifically to that series.

Just remember that I have a tendency to rant when let out of my cage, so please don't be offended by what I write.

1. - Summaries - This mainly pertains to Fanfiction.net, but it could also apply to people who post their fanfics on sites that include summaries next to the title. Basically, if there's going to be a summary of your fanfic, make it a good one. There are lots of people, I've noticed, who put in the summary, "I'm not good at writing summaries, so just read it, I know you'll like it." Most people just have a tendency to pass over stories that don't give a small plot summary to draw them in. Write your summary like you would a book blurb or a movie description. Get people interested in reading your story. This way, you draw readers who want to read the sort of stuff you've written, without also snaring the ones who like other things, or snaring the ones who would've passed over your story if you'd even had up a summary that said, "rape-fic featuring Shippo and Random Villager A," because they don't like rape-fics or pairing off Shippo with Random Villager A. I pass over stories that don't have summaries because I don't like yaoi/yuri fics, or fics that break up the canon pairings. I don't like to read fics about Kikyo, either, though I don't hate her. But also, when you write your summary, make it interesting. Make it hook the reader. Make it sound intelligent. Don't write, "Me and my sister fall through the well, and guess what, we're demons!" Blurb writers for novels don't write like that (blurbs are the summaries on the backs of novels). Movie writers don't say that on movie posters or in previews. Fanfic writers shouldn't say that either.

2. - Spelling - I find it annoying when I read fanfiction, well-written or not, with blatant spelling errors throughout. It's not really that hard to hit the spell-check button on your word processor, and if you're typing up your fanfiction in Notepad and have gotten people informing you of spelling errors in your work, switch to a word processor. If the word doesn't bring up any suggestions in the spell-checker, use a dictionary to check it. Also, some words may be spelled similarly enough to cause confusion for those who don't know how to spell. In that case, listen when people inform you that you spelled "does" as "dose," and other similar misspellings. Try to remember that you keep misspelling it. Graciously accept people's corrections. Heck, even get a pre-reader who knows how to proofread. It's not that hard, and you'll probably have more happy people in the long run. Also, double-check the spelling of some characters names. You can do this by listening closely to fansubbed episodes, where they're speaking the names in Japanese, or by looking at some of the better-made fansites (don't go to the one that just has a handful of pictures slapped up on a page with a gaudy background). They'll generally have at least one of the accepted romanizations. One mistake I saw (where the author accepted a correction and fixed it for the next chapter) was a misspelling of Kohaku's name (Sango's younger brother) to Koharu. If you listen to the Japanese, you can hear the second "k" in his name. And lastly, don't give excuses for not being able to spell. Just try to fix it.

3. - Mary Sue/Self-Insert - Not everyone likes to read self-inserts, a.k.a. Mary Sues, where you give yourself omnipotent (all-powerful) powers and knowledge, or make every character fall in love with you. Generally, the characters used in fanfiction, unless fan-made characters, already have a set way to act or react. Many of these wouldn't do something along the lines of falling head over heels and exclaiming, "Oh my gosh, you're so beautiful, will you marry me?" the minute they see you, the author, in the story. Many of the characters I've seen this done to would never fall in love, or never fall in love with the type of person the author portrays himself/herself as, or already have someone they're deeply in love with/married to. As for the super powers, stories are much more interesting if the main character (in this case, the author) can't do everything. If every time the characters come across some obstacle, the self-insert character walks up and says, "Oh, I can handle that," and does, it gets boring. You might give yourself one or two powers, if the story allows for it (i.e. writing an El-Hazard self-insert would give you one special power, but it's not always the greatest power ever, and often has limitations), but don't make yourself into Superman in a world without kryptonite.

4. - OOC (Out of Character) - Try to watch how you portray characters. If you're writing an Inuyasha fanfic, and suddenly Inuyasha is all mushy-gushy over Kagome (or worse, a fan-made character) without there being plausible reason for it (i.e. mind-control), long-time fans of the series are annoyed. I've seen this a lot in the "Characters from [insert series here] join me for a game of Truth or Dare" fics, namely the Inuyasha fics. I can't even see Sesshoumaru and Inuyasha willingly participating in a Truth or Dare game, let alone allowing themselves to strut around in bras and kiss characters they've never shown any interest in. Also, with the fics where Naraku falls in love with Kagome (Naraku doesn't love anyone, but he does obsess over Kikyo), or Sesshoumaru falls in love with Kagome, etc., a lot of these pairings involve characters who would never fall for each other, and this makes them OOC. Also, don't have characters suddenly turn to each other and say "I love you" just because another charactuer (usually fan-made) said so. Also, Kagome would never become anorexic or suicidal just because Inuyasha isn't noticing her (he doesn't notice her for most of the series, but all she ever does about it is go home and maybe cry).

5. - Non-Canon Pairings - This is sometimes similar to OOC writing. Generally, if there's no doubt as to a pairing being canon in a series, don't try to pair them with other characters in your writing unless you're absolutely certain without a doubt that you can write it amazingly well. I've heard this especially from people who have read Slayers fanfiction where Lina or Gourry is paired up with someone who isn't Lina or Gourry (i.e. Lina x Zelgadis fics, or Gourry x Amelia fics, etc.). Anyone who has seen Slayers Next knows without a doubt that Lina and Gourry are a canon pairing, and a lot of serious Slayers fans will get annoyed at any pairings that break up Lina and Gourry. This is similar to the pairings in Inuyasha that put Inuyasha with anyone other than Kikyo or Kagome, or Miroku with someone other than Sango, etc. It's most annoying when it's pairing a character who already has a canon pairing with a fan-made character.

6. - Yaoi/Yuri - First, yaoi and yuri are guy x guy and girl x girl pairings. Sadly, this partly goes along with non-canon pairings, and sometimes with OOC. I personally am annoyed by anything written like this, but that doesn't mean I will tell you not to write it. Just make sure, like with anything else, that you can write it well. I also find it especially annoying when the yaoi pairing is a pair that would never look at each other in that way, such as Sango x Kagome, or Miroku x Inuyasha, or, frighteningly enough, Sesshoumaru x Inuyasha and Naraku x Miroku.

7. - Rape-fics - I'm most annoyed, like Hoowee, with the rape-fics, especially where the character being raped (usually female) realizes they love the person who raped them. Rape isn't fun, and usually ends in lawsuit or trauma, not in true love. I saw a fic at Fanfiction.net that had Sesshoumaru rape Kagome, and end up with the two of them as a pair. ::shudder::

8. - Deus ex Machina - Deus ex machina is basically using the hand of God to wrap up a story. I've seen this done most often when a writer gets bored with their fic and doesn't want to write it anymore, but wants to end it. So they have someone come in, fix everything, and leave. The worst one of this I've seen so far is a fic (that mysteriously enough was an Inuyasha/Fushigi Yuugi crossover, where FY really had no business being in there) where Sango had a daughter (fan-made character) who showed up. The whole fic (I think it was around nine or so chapters by the time of completion) centered around the characters not knowing who the girl's father was. I only skimmed it, but even then, I couldn't pick up how Fushigi Yuugi fit in there, but I'll address that under "crossovers." A chapter before the end, the characters still didn't know who the girl's father was (this story also really had no plot, other than showing the girl around Sengoku Jidai), but the girl had mentioned that Kagome marries Sesshoumaru in the future, so of course Kagome, who had previously shown no interest, and Sesshoumaru, who had also previously shown no interest, went off to be alone for a while. Then, in the last chapter, the girl played Deus ex Machina. She told everyone who marries who (those couples then immediately professed their love to each other and were married), fixes the problem of Kagome, who's supposed to marry Inuyasha instead, and announces that she's remembered that her father is Miroku. Miaka summons Suzaku and sends the girl home. Big deus ex machina. Big no-no. Don't do that. It's boring, dumb, and will probably get you a lot of flames from people who go, "what the?"

9. - Crossovers - If you're going to do them, do them well and creatively. Don't write a crossover between two series just for the heck of it. Don't write a fic in one world and throw in characters from another just because you wanted to write a romance/action/comedy/whatever fic about those other characters as well. Try to find a connection. For instance, the only thing Inuyasha and Fushigi Yuugi have in common is the fact that Miaka, Yui, and Kagome all are transported back in time/to a different world. Fushigi Yuugi takes place primarily in ancient China, in a book. Inuyasha takes place in feudal Japan. The characters wouldn't run into each other. On the other hand, if you want to write a fic about Miaka falling into the well instead of Kagome, or Kagome reading the Universe of Four Gods instead of Miaka, go ahead. Just make sure you pay attention to what you're doing.

10. - AU/Alternate Universe - AU's are fairly easy to write, because they usually take just the characters and completely alter the plot/setting/etc. However, be careful with what you're doing. Stick to how the characters would act unless you warn folks at the start that you're going to do some of it OOC. Also, pay attention to matters of setting and plot. If the only AU thing you're doing is putting the characters in New York City instead of Japan, and having them attend college instead of search for shikon shards, but this NYC is in the real world and not some alternate reality where things are different, don't have characters with magic, or characters as slaves (I saw one that had college students owning slaves, without explaining why people in this world had slaves). You will drive readers away with inaccuracies.

11. - Criticism - Take it like a man (or woman). If it's downright flames, ignore them, or post them in a "Hall of Flames." Don't retaliate to them. For those who don't know, flames are people writing to you saying, "your writing sucks, your story sucks, why don't you go drown yourself?" or something along those lines. Not constructive criticism. However, if you're given constructive criticism (i.e. "it's a good idea, but you got this character's name wrong and that character's personality wrong, and they wouldn't have this item yet"), listen to it, see if you can use it to improve, and thank the person if they're polite. Don't retaliate. People are generally trying to help you when they criticize your work. Let them.

12. - Sequels - Sometimes sequels aren't the best way to go. Yes, you had a great fanfiction there, with beautiful writing and plot development, and a wonderful denoument, and suddenly someone mails you with, "what, that's the end? It's over? I want more! It's great! You should write a sequel!" Don't. Not unless you already had an idea for a sequel that works without rehashing the same plot or getting repetetive and boring. Don't write a sequel because some fan or other says to. Write a sequel because you have an idea for a sequel that makes a good story. If you don't, don't write a sequel.

13. - Description - There are three parts to this one.
    
    First, include discription in your writing. Description, especially to help set up a scene, makes the story flow better, and often gives the reader a good idea of the scenery (so they can envision the story better, increasing the enjoyment value). Don't get too expansive in your description, going on for a page and a half about how blue one girl's eyes were, but also don't limit yourself to just a "he said, she said" style of writing. The first is tedious, the second boring. If you want a good idea of how to set up good description, read a book.
    
    Second, be careful in your descriptions. Pay attention to how characters look. For instance, hanyou Inuyasha has white/silver hair, amber/yellow eyes, and wears red fire-rat fur (though in the earlier manga it's pinkish). Human Inuyasha, on the other hand, has black hair and steel grey eyes (or black if you're looking at screencaps of the anime). His human eyes aren't purple. Kagome, on the other hand, has black hair, and brown eyes (anime) or grey-blue (manga). Again, not purple. This is the biggest mistake I've seen made, from people who don't pay attention to colors when they start writing.
    
    Third, watch (and moderate) the words you use to discribe things. You don't need to find poetic words for everything you say, especially if you're writing simple fiction rather than a poem. I've lost count of the number of times I've seen "orbs" used in place of "eyes," or "locks" or "waves" in place of "hair." With "orbs," it just sounds weird. Stick to "eyes." You can't go wrong with "eyes," and if you actually read books, you'll notice most published authors use "eyes" every time they describe a character's eyes. With the hair description, use "locks" or "waves" once, and then stick to "hair." And make sure your readers know you're discribing a character's hair. Just because you have a thesaurus doesn't mean you need to use it every single time.

    - Language - Generally, the language you use when writing, and the language used by the characters.
    

    First, when writing. Don't use "kewl" or "leet" or "7337" words when writing. It annoys most sensible people, and confuses those who aren't used to reading it. If you've got an idea for a great fanfic, but don't know how to write in normal English, take an English class. If you "really need to get that fanfic out now 'cause it's so kewl," dictate to someone else, or get someone else to translate your "kewl" story into a "cool" story. Stories are always better in normal English. "kewl" language is okay if that's how a character talks, though, like L33t Guy in Megatokyo (who always speaks in l33t, with subtitles).
    

    Second, language used by the characters. The biggest problem with this that I see is people throwing random Japanese into their stories. It's generally all right if a character speaks in Japanese, and if you're limiting their Japanese to words like "hai." However, generally, when writing a character who speaks a language other than English, you either write what they say entirely in their own language, or entirely in English. Not half and half, unless it's a comic where sometimes the reader shouldn't be able to understand the character unless they speak that language as well. The part of this that most annoys me is when I'm reading a fic where the characters are even saying "yes" in English, and suddenly one runs up to another and asks, "daijobu desu ka?" Some fic readers proably won't understand that, and it sounds out of place among all the English. Yes, I know you've learned some new words in Japanese from watching anime, and don't you feel special? But just because you know it doesn't mean you need to include it in your fic, unless the character is an Otaku who throws random Japanese into their conversations. Some other exceptions to this case would be using Japanese words that really have no good translation in English, and thus work better if adopted as a new word (like "youkai," or "osuwari"). The case with "osuwari" is made because that word is used specifically for dogs in Japan, but doesn't have a real good English equivalent, since Americans only have "sit." A good alternative to the Japanese is how Viz translated the word, making it "sit boy."

    - Making Up History - Be careful when you make up history for an anime series. For now, it's all right to make up fanfics about Sesshoumaru's mother, since there's no real canon history for her written by Takahashi-sempai as far as we know (she may have included it in a magazine somewhere). However, coming up with a history for something like the Shikon no Tama doesn't work, since it exists already. You'll just annoy other fans.

    - Assumptions - This is similar to making up history. Be careful when you assume connections between characters that aren't canon, or how certain things work. For instance, assuming where Sesshoumaru's facial markings come from, or that someone has to be dead for him to use Tenseiga (Jaken wasn't dead when Sesshoumaru sliced him), or that Rin is oppressed and hates Jaken, who always tells her to shut up (yes, he's strict with her, but he isn't mean, and she's always cheerful). You could easily annoy someone if you assume wrong.

    - Be Prepared/Take Notes - This means taking notes both on the series you're going to write a fic in, and taking notes on your fic as it stands already. Be prepared to write a fic about a series. Watch what you can of it, and take notes on who characters are and what relationships they have to each other. If you want to write a fic based on early episodes, indicate so, but also don't come up with too much stuff that might be covered later if you haven't watched later episodes (like people who've only seen up to where we meet Sesshoumaru, but not as far as actually being in Inutaisho's grave, and thus write fics set later where Sesshoumaru still has his own left arm). Take notes on what happens, the history of some things, and decide whether you're going to use filler or not. Also take notes on what you've written so far, and constantly re-read what you've written, so you don't forget a detail later in the story.

    - Traveling Through the Well - This one is an Inuyasha (and crossover) only one.
    

    Please note if you're writing fics about Inuyasha that there are limitations to the well. From reading a fansite about Inuyasha, and discussions on a message board, I've come to a few conclusions. First is that only Inuyasha and Kagome can travel through the well without a traveling buddy. Kagome doesn't need shards to get home through the well (Yura and Inuyasha have both pushed her through without shards). She needs shards to get back through (the first time, Inuyasha took her back, and the second time, Shippo had the shards at the bottom of the well on the Sengoku Jidai side). The well can be blocked, but depending on what it's blocked with and how it's blocked, Kagome may still be able to cross through if she has shards (when Inuyasha blocked it with a tree, she still got through once Shippo brought the shards, but when tree roots blocked it in the first movie, the roots blocked it on both sides and Kagome had to shoot her way through with a miko's arrow). Other people can't get through without a traveling buddy (either Inuyasha or Kagome), and may or may not be able to get through with a traveling buddy (we haven't ever seen them try). They can't get through with the shards, as Shippo fell down the well with shards and didn't travel through (though the tree blocking the well might've had something to do with that, I doubt it). However, Yura's hair got through the well because it was attached to Inuyasha when he went through to fetch Kagome, and even then Yura herself didn't try to go through, she only sent her hair. The centipede demon's bones (and assumably soul) were in the well in Kagome's time, so she simply had to return home through the well (which it seems anyone can do if they get through it in the first place). If, however, this is incorrect, the centipede demon was also holding Kagome (who had the Shikon no Tama in her body at the time) as Kagome fell through the well, so that would fulfill the "traveling buddy" requirement. Inuyasha, it seems can travel through the well without shards with no problem, except for that one time I recall Kagome using an arrow to seal the well.

    - Osuwari! - This is another Inuyasha-only one. There's two things with this.
    

    First, Kagome isn't abusive with "sit." She's only used the multiple "sit" twice (once in the series and once in the first movie), which seems to be extra painful. The first of these knocked out Inuyasha's back. Usually, Kagome only uses "sit" when Inuyasha is being a big baka. She doesn't do it for every little thing, like calling her "wench." She usually just ignores these. Too many fanfic writers have her yelling "sit" for every little thing, or using multiple "sits" several times in a row (where she probably wouldn't use it at all), and one writer even had her "discovering" that if she modulates the volume and length of "sit," it changes the angle of Inuyasha's plummet and the force of the fall (the first of which is highly unlikely, given laws of physics).
    

    Second, there's who can say "osuwari," and get Inuyasha to "sit." Kagome definitely can, but judging from other characters saying "osuwari" around Inuyasha and him not falling, we can safely assume no one else can. But what if Kagome had a child who inherited her miko powers? I don't think that child would be able to make Inuyasha "sit," since it appears that yelling "osuwari" is not one of Kagome's miko powers. If it were a miko power, Kaede would be able to say "osuwari" and make Inuyasha "sit," but she obviously can't. We know she has the powers of a miko because she and Miroku together (and she herself on occasion) are able to create a barrier. So basically, Kagome's children should not be able to make Inuyasha "sit."