I visit this forum, read Lara's many threads on the topic, then I tell myself 'just write'.
I also play this YouTube lego movie which makes me laugh.
http://www.youtube.com/watch?v=eTpdlrBKphM
Other tips I've had - take a break.
- go for a walk or a bike ride
- phone a friend
- watch a movie
- tidy up
- look at photos
That way, you'll stop thinking about not thinking and come back to things fresh.