"Stop thinking, start writing"
In a recent Writer's Digest, Gruen, the author or Water for Elephants, said that was what she told herself when she was trying and failing to write. I think it perfectly sums up my own writing struggles, when they occur.
(Though luckily now is not one of those times! I'm working on a short story and enjoying it, and I have an idea for the novel I want to pursue in November for NaNoWriMo.)