I get bad insomnia - six hours sleep is a good night for me so I'm very interested in this. I have some tips that help.
Firstly, keep your extremities warm (hands and feet, silly!). This improves circulation and thus hastens sleep.
Secondly, keep your lips closed but your teeth slightly apart, and don't let your tongue touch the roof of your mouth. (If your teeth are together or if your tongue touches the roof of your mouth, this means your facial muscles are not relaxed! This makes it much harder to sleep.)
Thirdly, cut out drinks with caffeine in. When I get home I only drink Green Tea.
Fourthly, try a bit of light exercise. Occasionally I will walk a mile or two on the way home from work, then get a bus or cab. Seems to help.
As I say, though, I still get insomnia but those things do help a bit.