1. Lie on your stomach and turn your head so that your right cheek is on the pillow (or the bed as you prefer). This will automatically free up your left nostril to bring in the cooling, soothing and calming energy.
2. Start long deep breathing, inhaling maximum, exhaling maximum. Of course, you are ONLY breathing through your nose, keeping your mouth closed. Breathe consciously. Concentrate on making each breath as long and deep as you can. Think the sound SAT as you inhale, and NAM you exhale.
3. After a few long deep breaths, use your arm or hand to completely block your right nostril. Continue long deep breathing only through the left nostril.
4. When you feel yourself reaching a slight stage of drowsiness, which usually takes about ten complete breaths, turn over onto your back or your side as you wish, depending upon how you are most comfortable. Continue long deep breathing until you are fast asleep! By the way, it is better for your heart and your digestion* to sleep on the right side than the left. Plus, of course, it keeps your left nostril open. As soon as the breath becomes regular and slow, you will go quickly through the preliminary stages of sleep and almost immediately reach the deep dreamless sleep state, avoiding the energy draining dream stage altogether. Plus you'll be able to come back out of deep sleep more easily, and gracefully when it's time to wake up. from Shakti Parwha Kaur's book "Kundalini: The Eternal Flow of Power"

* One Ayurvedic source says that sleeping on your right side is better for digestion.