You may think good and fanfiction can't be in the same sentence together, and if you look at some of the stuff people post online (My Immortal, anyone?) you may have a point. However, many people enjoy writing fanfiction, myself included, and it's been that way for years even before the Internet. Some of these unofficial or non-canon stories are well-loved by fans and there's no reason you yourself couldn't pen the next great fic to go down in fandom history.
In a very broad sense, we write fanfic for many reasons:
- We are looking to practice our writing or get started as a writer.
- We feel we can do a good job of writing in a world which we love.
- We simply get inspired to tell stories not seen in the actual canon.
Through writing, you will also learn what it feels to love what you're writing about. This is a very key element necessary in creating original works of your own. And of course, you can and should learn the basics of setting up scenes and characters for your own ideas, which fanfiction can teach you how to do.
When you write fanfic, you should write what you want and how you want, because there's no better use of fanfiction than to test the waters of reception for any given idea. If you are going to be a serious writer, you would do yourself a disservice following the popularized "rules" of fanfiction, such as pairing your original characters with actual characters, creating powerful characters, or alternate realities. You should simply strive to write characters in situations you would find fitting to them while keeping the whole thing interesting and enjoyable to your audience. Many of the best fanfics out there are the ones that don't follow the rules.
Still, you should try to follow these basics, as always:
- Use proper grammar and spelling
- Stick to one style of writing. If you're going for 3rd person omniscient, don't switch to first-person mid-story.
- Try not to make the whole thing one big porno. At least add some feelings and conflicts and stuff.
- Don't write "drabbles"... you cheater!
- Write as if you were gonna' sell the thing (but stop short of actually selling it)
- Don't publish your fanfic if the author of the original work has expressed that they do not appreciate it.