okay, wehn trying to sleep, i don't think of anything important...or at least, i try not to.
If i do, it's game over, get up, and start again. (i think of myself as a periodic insomniac, which is why i'm still up at nearly midnight)
If i'm going to think of anything, it's about going to sleep. I close my eyes, and envision myself walking into a dark shroud that is sleep, and into my dreams.
Gradually i lose all sensation of my body, and then i'm asleep, and then i know nothing till the morning, when i wake up and remember my dreams.
If i find i can't sleep, i write in my journal, or listen to music, sometimes that helps. If that doesn't work, i usually hang around on here...

Hope this helps!

PS, don't lie there thinking about the Gas Bill!
(i've done it... )