Wow, I'm up against that one quite a bit as part of my job.
One things I've finally learned to do after all these years is to make notes when I've got something running in my head and the deadline ISN'T zooming right up on me. That whole "oh, I'll remember this later" headspace can really leave you in the lurch at the last minute.
I try and make my writing environment comfortable as far as temperature, needed supplies (either for writing or me) and free of as many distractions as possible. I like to play instrumental music softly in the background. It's not deadly quiet that way and the lack of words is less distracting.
Ever notice how suddenly you are into cleaning your whole house when you have something to write and it won't come out of your head? If I'm getting into avoidance behavior, I'll take a quick walking break, where I go around the block and clear my head. Often the walking and thinking gets me unstuck and I can get rid of the "trapped with my writing" feeling.
- Rae