Since breathing is something we can control and regulate, it is a useful tool for achieving a relaxed and clear state of mind. Breathing exercises can reduce stress, improve mood, and help you feel energized. Better yet, they are simple, easy, and can be done anywhere. I recommend four breathing exercises to help relax and reduce stress: Improving Exhalations, Stress Reducing Breathing, Breath Counting, and Stimulating Breathing. Try each one and see how they affect your stress and anxiety levels.

Exercise 1: Improving Exhalations
One way to promote deeper breathing and better health is by exhaling completely. Try it: take a deep breath, let it out effortlessly, and then squeeze out a little more. Doing this regularly will help build up the muscles between your ribs, and your exhalations will naturally become deeper and longer. Start by practicing this exhalation exercise consciously, and eventually it will become a healthy, unconscious habit.

Exercise 2: Stress Reducing Breathin
Although you can do the exercise in any position, sit with your back straight while learning the exercise. Place the tip of your tongue against the ridge of tissue just behind your upper front teeth, and keep it there through the entire exercise. You will be exhaling through your mouth around your tongue; try pursing your lips slightly if this seems awkward.

1.Exhale completely through your mouth, making a whoosh sound.
2.Close your mouth and inhale quietly through your nose to a mental count of four.
3.Hold your breath for a count of seven.
4.Exhale completely through your mouth, making a whoosh sound to a count of eight.
5.This is one breath. Now inhale again and repeat the cycle three more times for a total of four breaths.

Note that you always inhale quietly through your nose and exhale audibly through your mouth. The tip of your tongue stays in position the whole time. Exhalation takes twice as long as inhalation. The absolute time you spend on each phase is not important; but the ratio of 4:7:8 is. If you have trouble holding your breath, speed the exercise up but keep to the ratio of 4:7:8 for the three phases. With practice you can slow it all down and get used to inhaling and exhaling more and more deeply. Practice at least twice a day. You cannot do it too frequently. Do not do more than four breaths at one time for the first month of practice. Later, if you wish, you can extend it to eight breaths. If you feel a little lightheaded when you first breathe this way, do not be concerned; it will pass.

Exercise 3:  Breath Counting
Sit in a comfortable position with the spine straight and head inclined slightly forward. Gently close your eyes and take a few deep breaths. Then let the breath come naturally without trying to influence it. Ideally it will be quiet and slow, but depth and rhythm may vary.

• To begin the exercise, count "one" to yourself as you exhale.
• The next time you exhale, count "two," and so on up to "five."
• Then begin a new cycle, counting "one" on the next exhalation.

Never count higher than "five," and count only when you exhale. You will know your attention has wandered when you find yourself up to "eight," "12," even "19."

Try to do 10 minutes of this form of meditation.

Exercise 4: Stimulating Breathing - A Mental Energizer
If you need a pick-me-up or are feeling a bit anxious, try the following breathing exercise; it can help to bring energy and clarity to your mind. The first time, do it for just 15 seconds, increasing the duration by five seconds every time until you can complete one full minute. Always breathe normally between exercises.

• Sit upright with your back straight, eyes closed, and shoulders relaxed.
• Place the tip of your tongue against the bony ridge behind and above your upper teeth.
• Breathe rapidly through your nose, in and out, with your mouth slightly closed.
• Keep your inhale and exhale short and equal. Your chest should be almost mechanical in its movements - rapid, like air is pumping through it.
• Try to inhale and exhale three times per second, if you can, keeping your breath audible.

Ideally, you will feel the muscular effects of this breathing exercise at the base of your neck (just above the collarbone) and at the diaphragm. Put your hands on these areas to get a sense of the movements.

Source: The Art and Science of Breathing by Dr. Andrew Weil, M.D.