1. Lie down on a blanket or rug on the floor. Bend your knees and move your feet about eight inches apart, with your toes turned slightly outward. Make sure that your spine is straight.
2. Scan your body for tension.
3. Place one hand on your abdomen and one hand on your chest.
4. Inhale slowly and deeply through your nose into your abdomen to push up your hand as much as feels comfortable. Your chest should move only a little and only with your abdomen.
5. When you feel at ease with step 4, smile slightly and inhale through your nose and exhale thorough your mouth, making a quiet, relaxing, whooshing sound like the wind as you blow gently out. Your mouth, tongue, and jaw will be relaxed. Take long, slow, deep breaths that raise and lower your abdomen. Focus on the sound and feeling of breathing as you become more and more relaxed.
6. Continue deep breathing for about five or ten minutes at a time, once or twice a day. Then, if you like, gradually extend this period to twenty minutes.
7. At the end of each deep-breathing session, take a little time to once more scan your body for tension. Compare the tension you feel at the conclusion of the exercise with that which you experienced when you began.
8. When you become at ease with breathing into your abdomen, practice it any time during the day when you feel like it and you a4re sitting down or standing still. Concentrate on your abdomen moving up and down, the air moving in and out of your lungs, and the feeling of relaxation that deep breathing gives you.
When you have learned to relax yourself using deep breathing, practice it any time you'd like, but especially times when you feel yourself getting tense.
Exercise from Relaxation For Dummies by Shamash Alidina