That's why I never go to bed until I am sleepy. I just sit up until I feel I could sleep. I end up staying awake and just sitting on the couch until 6am, not even concerned with sleep. Then I get sleepy and lay down. I'm out as soon as my head hits the pillow.
i learned that the hard way...it's cool, now, though..i just imagine how nice it feels to be done with the day, and just lose myself. i usually listen to some relaxing music, too...
deep breathing exercises (usually works for me) nursing your baby (if your are a momma) taking a hot relaxing bath with some aroma thereapy
oh and another one I find works is just to lie down and picture yourself in a beautiful place you've been to like a particular day or valley or a field and walk around it for a while - explore its hidden groves and ditches and nooks and crannies and sit under a tree but stay there a while - the key is really visualise it and relax there as if you are there