Ugh, I used to wrestle with this too. Tried weed, but I was just laying there high. With PM's if I don't fall asleep immediately, I instead start fretting. Whiskey is a nice conversation around camp, and it helps me chill out.
But I came to deeply appreciate that rest is a physical and mental state. So, simply lying prone and mentally relaxing, was a greater part of what my body and mind needed, which led to sleep. And I stopped struggling toward sleep. Honestly, I don't even really focus on it, I just lay there and appreciate where I am.
I really discovered this when I started sleeping out in the open, without a tent, in full connection with the place I was in. It sounds corny, but when I'd wake up in the night, I could smile at the expanse of stars, smell the earth and the wind. Enjoy everything that comes with that sense of peace. A tent sort of disconnects me from that.
So, connect yourself with the place you've chosen and relax there.
And, hey, use some truly relaxing bed time herbs. Get some chamomile, sleepy-time teas. They work if you let them. Once again, just relax.
cheers,
-Michael