Helpful Advice for writing fanfiction (or any other type of story):

If you are not completely sure what a word means, look it up. Especially if that word is in another language. Google, Yahoo, Answers(.)com and other search engines are your friends. If you are writing a story you should write it as best as you can.

Don't use words in another language unless completely necessary and you either are fluent, have a trustworthy translator a click (or arms reach) away, or your beta/proof reader(s) can help you. This is more of a guideline than a rule though.

Get a Beta/proof reader. Sometimes more than one. This is simply because even if you have memorized all grammatical/spelling rules (and/or exceptions) when it comes to your language (and/or the one(s) you write in) that does not mean you do not make mistakes. All of us makes mistakes, it's part of being mortal.

Don't dismiss bad reviews automatically. If they provide no reason or advice and just say things like "OMG! U SUCK!" or "THIS STORIE IZ TEH LAME!!" over and over again, then you can go ahead and dismiss/politely ignore them. However, if you can find any bit of advice for your writing, then take it and absorb it. You don't have to respond, just make sure you read and take what you can from it. This is what separates the authors that will always be bad from the authors that have the potential to be good, and the authors that are good from the authors that have the potential to be great, and the great authors from the ones that have the potential to be Awesome.

Common Mistakes in spelling in fanfiction that really shouldn't be common:

Bleach:

Misspelling Zanpakutou as Zanpaktou, Zanbaktou, or something similar. Just because the "u" between the "k" and "t" is silent doesn't mean it's not there. Seriously, I've made no less than 10 reviews stating that it's Zanpakutou, not zanpaktou or zanbaktou. Regardless of the early translations misspelling it in the manga, they are wrong and have since been corrected.

Misspelling Kisuke as Kiske. Same thing as Zanpakutou.

Misspelling Shinigami as Shishigami, Shikigami, Shimigami, or Shinegami. I'm pretty sure Shishigami is really just a character from Princess Mononoke, while a Shikigami is something completely different. I have no clue what a Shimigami would be, and all I know about Shinegami is that it's completely wrong.

Misspelling Reiatsu as Reitsu.

Naruto:

Misspelling Inuzuka as Inuzaku or Inizuka.

Misspelling Aburame as Aburami or Abirame.

Misspelling Tsunade as Tsunande, Tsuande, or Tsuniade.

Misspelling Chakra as charka or some thing similar. Both are technically incorrect anyway, because it's spelled "Chakura" by the Japanese. Most likely because they don't have a "k" by itself in their alphabet.

Misspelling/misusing Bunshin as Bushin. Bushin doesn't mean Clone/Doppleganger; Bunshin does.

Misspelling Hitai-ate as something else like Hi-ate, or Hitei-ate.

Misnaming various people, such as Morino Ibiki being misnamed as Morino Hibiki.

Things brought about by Fanon:

Naruto:

Naruto being a Saint-like being/person in the beginning: Naruto was not a good, saint-like guy in the beginning of the manga. He was just as much an asshole as Sasuke, and had just as many flaws as the rest of the Team. Naruto was an arrogant, over-bearing, self-centered, moronic jerk in the beginning of the manga. Over time he has improved drastically, just like Sakura has. However, Kakashi has barely improved (he is still lazy, caught up in/concentrated on the past, and a number of other things I could say) and Sasuke seems to be have started going on a downward spiral since he got the Cursed Seal, which increased his agression and jealousy and negativity.

Rock Lee's mangled chakra coils: Rock Lee can use chakra (as evidenced when he walks on trees and water in the manga/anime). The misconception brought about by Fanon is that he can't use chakra because of mangled/destroyed chakra coils. However, he is stated, in canon, to have "no talent" for ninjutsu and genjutsu (by his teacher Gai and the Databook). "No talent" does not mean the same thing as "completely unable to use," despite what many people may say.

Sasuke saying "That power should be mine!": This is completely false. Not once did Sasuke rage over somebody else getting/having a power that should "rightfully be his because he's an Uchiha" or something, at least not that I can recall. He only started to show extreme pride in being an Uchiha in Part 2, and before that showed pride in his Sharingan, and the pride in his Sharingan is rightfully earned (though it's a bit excessive). The Sharingan is an extremely powerful tool and bloodline limit, no matter what others say. Sasuke has said "What is this power!?" before, but not "That power should be mine!"

Naruto being beaten before Canon/as a child: There is no proof for this whatsoever. We know he was ignored and disliked/hated, but we do not know if he was beaten.

Naruto living in a crappy, broken down, old and moldy apartment with graffiti on the walls and broken windows and other various things: This is completely incorrect. In fact, in the databooks, there's a floorplan of where he lives and it's a rather nice, big place, if a bit sparse. It looks a bit run down and somewhat moldy, but that could be because it's a sketch. The anime gives a bigger look into his apartment though, and that's based on the databook entry.

Orochimaru's last/family name being Mitarashi: Big fat Fanon. We don't know his family/last name. Besides, I'm pretty sure it was explicitly stated in canon (most likely databooks) that Anko was Orochimaru's apprentice/student, not his daughter or of any relation to him.

Naruto's obsession with Ramen: This isn't nearly as gigantic as many fanfictions make it out to be. I'm pretty sure that the first time this showed up was because it was done for humorous purposes. That...sadly, isn't how it is now. Now, it's just gotten ridiculous, cliché, and old. Make him like Ramen, make him love it, but please don't make him have it as the only thing he eats (nobody could live solely on Ramen, even a Jinchūriki), with him keeping Ichiraku's afloat by himself. That just can't happen. I'm starting to think that some of these author's have never eaten a bowl of Ramen, and/or read the ingredients and nutrition labels on them.

I will be updating this as I go along and come across them.

Lemons aren't allowed, strictly speaking, on fanfiction(.)net. You might want to back any stories containing them on another site, like ficwad, adultfanfiction, and/or mediaminer(.)org, just in case.