One thing that seems to be having a 50/50 success rate, is that about an hour before I want to sleep, I turn off the TV, and get away from the PC or anything backlit. And I've started going up to bed, getting comfortable, and reading on my kindle since it's e ink and not backlit. That way, if I get sleepy, I can simply put down the kindle, and turn off the light and sack out.
One of the biggest issues I have is getting my brain to turn off. I'll be tired, and lay down, but my mind is still going 100mph, with all kinds of thoughts racing through it. I've tried random things like counting sheep (sounds silly I know) but anything monotonous to trick your brain into lulling to sleep, and that doesn't work. I've tried music, but then I just focus on the words and stay awake till the radio timer runs down. Hmmm, maybe some classical?