I used to have that problem where it'd take me awhile to get to sleep. I think it was motly because I wasn't really that much tired, or because I liked to think before bed and couldn't sleep unless I had thought everything through. Then I had found a job where the hours were so long that when I did get into bed I was fast asleep. Ever since that job I seem to get to sleep very easily and it is seldom that I don't get to sleep fast now.
I would recommend trying to tire your mind out before you go to sleep as well as your body.