I've had insomnia for ten years now. Every once in a while, I get lucky, and this trick works:

Lay flat on your back. Imagine a great weight rolling slowly from your feet up to your head, and then back again. Keep doing this in an easy rhythm, and you'll soon be totally relaxed.

The idea is that, while imagining the pressure from the weight, you notice tense muscles and they relax.

--Jez"a half-glass of red wine helps me, too"zika