How to Write a Good Fan Fiction

I have no idea, first of all, if this was already created as a topic, and if it is I apologize, but after reading some fan fiction on this website and a forum I'm on, I just have to make this post.

So what I'm going to go over is some dos and don'ts for writing fan fiction. Understand, that just because an idea is kind of original, doesn't mean the story itself is.