Maintain good posture. Slumping your shoulders or staying in positions in which your upper body is thrust forward (many people do this to relieve back pain) disturbs the natural alignment between your facial bones and muscles.
Don't sleep on the painful side of your face. Avoid sleeping on your stomach.
When you sleep, use a single, flat pillow or a specially designed pillow to help keep your neck and head in alignment (ask your health professional about pillows).