The best way to combat your mind just not switching off is to simply stop trying. I've heard this being said many times but it has never been actively explained. For example if you can't sleep just get up and do something else.
Don't sit up in bed and read a book or watch a film in bed, get out of bed go into your living room and read or watch in there. It works for me everytime. Right now I am sitting up typing at 4am. Its also dawning on me that I may have done this blog before.
Anyway I believe the fact that you are completely removing yourself away from the bed helps taking your mind off sleeping. People may say 'oh but I have to get up in four hours' most likely you are going to be lying in bed for four hours doing nothing, might as well do something constructive.
It doesn't even have to be productive, watch a film you've never seen before or start that book that has been sitting on your shelf or play a computer game. Use that time to do the things that you never get a chance at doing even if they are completely pointless.
It works for me with good effect because before I know it I'm feeling tired again. Hope this helps, if not e-mail me and we can stay up late together and create an underground fighting club with our alter ego's our mind produced to help deal with our insomnia!
