When I can't sleep is is usually due to worry. I get a circular thought pattern going and I have to break it by forcing myslf to think of pleasant things. Things I like instead of things I don't like.

Also I relax by going completely limp, stretching out as far as possible and exhaling deeply. Like a balloon deflating.

Thirdly, a radio or TV with voices seems to distract my mind just enough to blank out thoughts. The sound from something like a fan helps some. I presume one of those sound generators that produce surf noises etc. would help too.

My wife says I coud go to sleep in a bus station. I frequently catch naps sitting on a bench in the mall while she shops.