Years ago I started making up mind games to switch off my over active mind.
So I tend to do games such as '50's' - this could be anything - think of fifty movies you've seen. Fifty actors, pop groups etc. For me, I usually don't get past thirty and I fall asleep. On bad nights I may go through a 50 favourite 'something' and go onto another, but I just keep going and you do fall asleep. But the trick is to keep it not too interesting. You don't want to stimulate your mind too much. You can also make the game as hard or as easy as you like.
I think this works - for me at any rate - maybe because you are switching your mind off to everything and focusing on one thing, so this tends to relax you more.