To write a fanfiction, only write when you have solid ideas that make sense. Don't tell a story that is everywhere and in-understandable. Use proper grammar, if you didn't know; some fan fictions get published someday, if you want that, PROPER GRAMMAR IS KEY.
Read other fanfictions and see what other people write about and get some ideas from that. Read different types of that topic of your interests. Or, come up with your own idea entirely.
