Lie on your back and breathe deeply.
Notice where you can feel your breath in your body. It may be in your abdomen, your neck, your feet. Focus your attention there, and notice where and when it moves.
Take three deep breaths, and notice your abdomen filling up with air and falling again.
Imagine you can see the air travelling through your body and out again, and breathe more softly.
Notice where you are feeling tension, and bring your breath to that place.
If your thinking mind takes over, bring your awareness back to your body.
Repeat three deep breaths whenever you notice tension and then soften your breath again.
Let everything fall away, and gently allow yourself to fall into sleep.