I know people have various troubles with going to sleep. I've rarely had problems, thanks in part to learning to sleep standing up in boot camp! But sometimes busy-ness or stress does lead to some problems with laying down and going to sleep.
I mentioned that the breath counting meditation isn't ideal for sleeping, since you want to maintain a big focus on the counting.
I'll toss you a simple example of a good going to sleep exercise. Remember that the thing to do with distracting thoughts is just acknowledge that they passed through and let them go.
Posture isn't really important for this one. There's possible variations, but just lay down however you usually fall asleep.
Close your eyes and build a picture in your head of your body as a city full of lights. Skyscrapers and houses and whatever. every light on. This gets easier, as most things do, with practice.
Once you have the image, begin by focusing on one foot and start turning off the lights and putting that part of the body to bed. As you turn off the lights, think of that part of the body being relaxed and heavy. You can switch to the other foot or move up one leg, whatever works. If you can just run with this, anything works. If you want more guidance on how to travel up the body:
I generally keep things balanced, so I'll switch from my left foot to my right foot, then move up to left ankle, right ankle, and so on, moving up the shins, calves, knees, inner and outer thighs, to the hips. Once you hit the core of the body it's time to expand a bit and turn off larger sections as you can, travelling up the chest. At the shoulders switch to the fingers, palms, wrists, and so on. Once you work your way back to the shoulders, move inwards to the neck and start turning off the lights in the muscles around your neck, jaw, and head. Next is the brain, you can work this with whatever internal vision you have of portions of the brain, and just turn them off.
It's pretty common to start spacing out during this and just fall asleep. That's the goal! There's no need to feel any sort of desire or accomplishment in getting through the whole body.With a bit of practice, you might not ever make it past your knees!
If, somehow, you've made it through the whole body like this, work it again, with a bit more focus on the feeling of heaviness and sleep as you move up.