Yep. I saw some article about "British naval vets share how they fall asleep anywhere instantly". TLDR: Body scan + mindfulness meditation. I'm sure being exhausted helps in their case too!

Body scan: Lying still in bed, you are relaxed, right? Not so much, actually. Start mentally checking individual body parts and you'll find a bunch of muscles tensed up for no reason at all. Let each one go loose one by one. Then check again and you'll find they can still go looser. It can take several passes to get to the point where your muscles are actually hanging loose.

Meditation: Yep. We're going to do the "Clear your mind and don't think about anything" routine. Never works, right? That's OK. The point is not to succeed in thinking about nothing. All you need to do is notice you're thinking about stuff and go back to thinking about nothing. Over and over. You don't need to "win". Just fail and restart again and again and again. You can repeatedly fail, can't you? ;) As long as you keep restarting, you're good.

Can also step it up a notch and use progressive relaxation. many youtube videos for that, too.