Author has written 1 story for Harry Potter.
Tips for Writing:
Characters: Why is it that protagonist is usually a knight in shining armor type with noble and chivalrous streak a mile long? Or a stupid, muscle-for-brains with happy-go-lucky attitude? (Cough*Harry Potter, Naruto, and One Piece Cough*) Seriously, I've lost count of how many protagonists follow this cliche. I generally like more realistic protagonists who are willing to dirty their hands to win. So many novels feature main characters who are the pillar of moral strength and always, always try to do the right thing. Seriously, these protagonists need to learn that in order to change the world, you need to dirty your hands. Intelligence and ruthlessness will get you further than righteousness and brash stubbornness.
Plot: Some of the greatest Fanfiction works are based around authors' interpretation of cause and effect. It's good to follow cannon plot but you must remember that sometimes your characters will undoubtedly different compare to their cannon counterparts especially if you are writing AU. As such, different personalities and experiences will be created which influences their actions. The great writers will realistically predict the actions and consequences of these characters and how it affects the plot.
Crossovers: So many crossover stories end up with a protagonist from one franchise end up in another but rarely make true changes. After reading nth story, you'll notice that despite a new element added in (the protagonist), the plot rarely diverges from the canon. Sure, the hero will make the challenges easier to conquer but does plot truly diverge? Does any key characters change? Do any of them die and therefore irreversibly splinter away from canon? No, such things rarely happen.
I've read literally hundreds of fanfiction stories since joining and I rarely come across stories that truly standout from others. Those few that I do come across, I make sure to review them.
Bashing: At first, I didn't mind so much but after reading numerous works, both good and bad, bashing really isn't that good. Sure, we all have frustrations against certain characters and love to see them get their due punishments but bashing will inevitably cause the quality of your writing to decrease. Bashing is far too direct. Too obvious. Make it so that these rather unsavory characters fall in natural way instead obvious curb stomp. Remember, revenge is a dish best served cold. Have patience in your writing and don't make it so that your protagonists lashes out indiscriminately whenever these characters interact.
Formal Language: Ties into bashing part. Authors must always be impartial. Remember that you are telling a story, especially so if using 3rd person POV. If you are using 1st person POV, it's ok to disparage unpopular characters since we are reading from a character's POV even if I'd advise you not to. Most common example is how authors fuck up their names or describe certain characters in obviously biased manner.
Examples: Dumbledore and Umbridge from Harry Potter becomes Dumbledork and Umbitch. It becomes rather tiring to read after a while.
Grammar: This is one of the most important. Seriously, when you read a work with shitty grammar, you'll notice that quality of the story such as its plot, character interaction, and dialogues suck. It feels as if it's written by a bratty 9 year old. Nothings kills interest than shitty grammar. If you can't read it, why bother at all? Makes the readers wonder why the author in question bother writing at all. It's not that hard to simply do a research using internet for proper grammar.
Organization: Some stories literally lump the entire thing into a single, gigantic paragraph without any breaks. Descriptions, dialogues, and others need to be separated from each other in order to make it easier for readers to read. Also, it's a proper grammar. If the author can't separate them, then it's a sign that the author sucks and thus the story quality sucks. Like I said, it's too hard to read so readers won't bother.
Summary: Summary is your sales pitch, your chance to grab the readers attention. If you can't write good summary, then less and less people will actually read your story. After all the work you put in, no one will bother cause you failed to grab their attention. Some authors just write "I suck at summary, just read inside" or "Bad summary" or "Don't like, don't read." If you write these, then you just failed to make readers interested. When I browse through fanfiction looking for good stories to read, I automatically skip over them. Why should I bother looking into them if the authors can't even write out decent summaries? In few cases I actually checked out the story, they literally sucked. It doesn't have to be long. Just make it interesting enough for readers to actually pay attention.