I fret and drink copiously. What do you do? Seriously, though, once I've gotten the fretting out of the way, DrumminMama's advice is right on. One other thing that helps me: write something that I don't have to write. For instance, if I have an article due, and notes are not coming together into narrative, I'll start messing with an article on free open source software that I've been kicking around in my head, or something like that. Procrastination can be a fabulous creative tool!
All good points, with emphasis on those which are more constructive. Manifestation is a wonderful experience ;-)