I am an anxious person and my mind does sometimes race when trying to fall asleep, but I picked up a visualization technique somewhere along the way that works for me.

Basically, I visualize a looping scene (kind of like a boring, relaxing animated GIF) until my brain gives up and goes unconscious. It's been different things over the years, starting with the memory of relaxing solo experiences (e.g. riding a bike along a segment of lakeside bike path on a cool, sunny day) and is now something more abstract (a 3D cube with different-colored faces rotating in a black space).