Try out stream-of-consciousness writing.

Stream-of-consciousness is a writing exercise in which you set yourself a time or length limit and just start writing down the first things that come into your head. However incoherent, bizarre, or embarrassing they may be. The idea is not to think consciously about what you're writing even for a second, but just to let your thoughts spill out onto the page however they may. It's a great way to clear your head, but also perfect for brainstorming - you might uncover something you didn't even know was on your mind! Set a timer for 5-10 minutes and give it a shot.