Oddly enough, usually writing...Let me explain. If I can't think of what to write for my current novel, I'll write some goofy shit I come up with instead. It still gives me writing practice and it eventually leads me to getting over it. Watching anime and tv, listening to music or reading novels or even exercising can get my brain juices flowing.

I use a combination of all of those things. Do whatever works for you, and if you haven't found it out yet. Try something new instead, maybe just write about how your day went and what happened in it. Then maybe consider what the guy you passed on the street is doing in his life, brainstorm and write about that. Make yourself be imaginative. If you dedicate enough time to it, you will eventually beat your writer's block, least from my experience.