Breath promotes relaxation. Relaxation induces sleep. Focusing on our breath clears our head. A clear head induces sleep. Try this Yoga Technique to help you fall asleep. Put your finger on your right nostril so that you cannot breathe in or out of your right nostril and now simply inhale and exhale through your left nostril. Try this for 3 minutes and then breath normally.
Sleep Tip #95: Breathe through your left nostril.