Mantras.

As you’re trying to fall asleep, repeat in your mind ‘I will awake at seven alert and refreshed’. (e: or six or five, or whatever, but keep a rhythm.)

If your thoughts are intruding, say it aloud. Keep your phrase to four beats (awake, seven, alert, and refreshed should be even beats). Keep saying or thinking it, over and over, until you fall asleep. Sync it to your breath and heartbeat.

It sounds stupid and simple, but it works.