When I lie down to sleep, I make myself accept that there’s only one thing I should be doing right now: Fall asleep. As random thoughts inevitably arise, I stay mindful of how they come, let them be, and see as they vanish. Then I get back to that sole task of falling asleep. Mindfulness is not a high-alert state, nor does it require much attention, but I sure can’t fall asleep multitasking.

The following article has motivated me to use this approach in more parts of my life as well. I endorse all of the techniques Colin describes:
Colin Wright: Out of Time