Author has written 21 stories for Harry Potter.
Bunnyhops (formerly SeverusMalfoyMaiden) here!
There are a few things I've learned since beginning this adventure in writing stories, which I would like to share (I'm also guilty of most of these as well):
1. People having conversations use contractions like I've, don't, won't, we're etc. use them in your stories. Otherwise, it feels like someone's reading off a cue card. very stiff.
2. Go back and reread your story. I know sometimes you get caught up in writing and put some minor detail in the chapter...then it turns out that that small detail contradicted with an earlier detail making your readers either confused or annoyed.
3. Flesh out your characters. I know JK already built the foundation for the characters we use, but in our stories we take artistic liberties and there are certain nuances specific to how we envision them. Let your writing reflect the quirks.
4. Write your chapter, save it and let it sit for a day and then go back and read it again. You'll prevent typo's, missing words and grammar errors this way... unless you use a beta then never mind.
5. Tenses. It's sometimes difficult to keep the story in the appropriate tense. Think about when an event is occuring and write it. Then reread.
6. Remember the human condition. Three people can watch the same event and remember it differently; write those deviations. It adds depth to your characters.
7. (these outstanding additions are courtesy of Severus49) Writers should know the difference between: breathe (to inhale and exhale) and breath (a singular inhalation); cloth (a piece of material) and clothe (to put on apparel); and Its (meaning ownership) and It's (the abbreviation for it is).
8. (more tips from the gracious alliehatescats) There, Their, and They're. there as in, it's over there; their as in, it's a persons posession (sp); They're as in, they are going to do something.
I think that's it for now, have fun. If you have more tips, let me know!