In her book "Breathe", Jean Hall includes a great breathing practice to induce sleep. The practice was pioneered by Andrew Weil, a doctor based in Arizona. Make sure you are tucked up in bed when you begin the practice.
1. Lying on your back, rest the tip of your tongue on the roof of your mouth, on the ridge just behind your upper teeth.
2. Exhale completely and let your body relax and sink into the bed.
3. Slowly inhale through your nose for 4 counts and then hold the breath for 7 counts.
4. On a count of 8, softly whoosh the breath out through your mouth, resting your tongue on the floor of your mouth.
5. Continue like this until sleep prevails.