I've always found free-writing to be very helpful in the past; to set aside whatever it is that I'm trying to work on and just start with a blank page and write whatever comes into my head. Doesn't always work, but often it helps just to get words on a page and clear my head. Occasionally, the idea I was searching for comes out in the free-writing space, most often though I clear my head there and find I'm better able to focus when I go back to the original project.