The best thing you can do is five hours before going to bed, making sure you get enough exercise and avoid caffeine.

Other than that, I have a routine of stretching and reading before bed, so usually just doing that puts me out.

Failing that, I used to have really bad insomnia, and one thing I would remind myself is that even just laying awake in bed is a kind of rest, and even if you don't sleep you can kind of drift off into a reverie here and there.

Related, I find having something enjoyable to think about as I close my eyes is fun and distracting. For me that's creative stuff like writing stories, designing games, or making game levels in my head.