Depends what you want to write but the biggie is involvement.
No matter what your subject is, become absorbed in it, participate, interact with people who are living that life, let your interest consume you, and the creative ideas will flow. Personally, I can't write from a distance: I have to get in close.
If you're writing fiction, learn as much about your subject as you can. The Internet is a wonderful research tool but it's not the only one. I knew of one successful author whose novels were all set in the South Pacific, which he had never visited. He learned it all from books. You can do something similar with any topic, be it historical, fantasy, sci-fi, or crime. Learn.
Your imagination thrives on the material you feed it.
Good luck. It's lots of fun.
