Providing I at least feel a little bit like sleeping, I have a system for getting there.
Normally, when I try to sleep I let my mind wander. I think in words and I can get carried away thinking of shit and because my brain's working at 100mph it takes ages until I burn out and go to sleep.
When I TRY to sleep, this is how I do it:
Lie in a comfortable position. Usually I lie on my back with my hands over my waist, or on the bed.
Focus on your breathing. Breathe slowly. Think about how slowly you actually breathe when you're sleep and gradually, maybe over 30-60 seconds slow your breathing to this sort of speed.
Now, relax your head, and your face muscles.
relax your shoulders
relax your chest
relax your arms
relax your abs
relax your waist
relax your upper legs
relax your lower legs
relax your feet
The end result is you're lying there with your body feeling like dead weight.
Now, try not to think of too much. I'm shit at picturing stuff but I try to picture doing something, going somewhere. Thinking a little bit is ok but try to keep tabs on it.
Always keep breathing slowly.
You might sort of snap in and out of awareness, you're aiming to go out but sometimes you do just snap aware again. If it happens just keep at the original goal - not too much thought. Try to sort of feel for when you're drifting off and kinda encourage yourself to do it. Try to gently become absorbed in whatever you're picturing.
I don't always do it but it helps me get to sleep quickly if I need to. It even works when my mind is f**ked. If you're not at all tired it might not work.