Relax, close your eyes, fall asleep. Not much to it other than making sure you're not in a position where your arm will fall asleep or neck gets cramped. There's no secret to it, you just go to sleep.
I feel extremely lucky to fall asleep in 5 minutes very regularly. It takes my wife a few hours to fall asleep, we’re polar opposites in that aspect. Maybe it’s genetic, my grandpa and father both fell asleep quite easily.