The only thing that works for me (and works like a dream) is to stop worrying about whether or not I'm going to sleep. Instead I just enjoy lying quietly and letting my mind run loosely wherever it will. I figure if you lie quietly and mentally drift then you are getting almost the same benefit as if you did so unconciously.
Its a technique I have perfected on noisy festival campsites - sometimes it drifts you off to sleep anyway, but if it doesn't then you still get up feeling rested and ready for the day.

KRis