1. Diaphragmatic or abdominal breathing induced by lowering and flattening the dome-shaped diaphragm causing the belly to protrude..

2. Intercostal breathing brought about by expanding the rib cage as the belly comes inward to force the breath upward.

3. Clavicular (collar bone) breathing from the top of the lungs, produced by raising the upper part of the thorax as the belly gets pushed inward and upward driving the diaphragm higher up into the chest.

Supposedly each of these phases has its own merits, but in theory yogic inspiration is only complete when all four are done in proper sequencing  This by the way has little to do with optimal natural breathing.

First of all they say one needs to practice breathing from the diaphragm.

1. First empty the lungs by extending the exhale by forcing breath out by strongly squeezing inward the belly muscles towards the spine and upward into the chest cavity.

2. Slowly breathe in allowing the belly to relax and enlarge and the diaphragm to lower and allowing air to enter the lungs. When the abdomen swells the hope is that the bottom lobes of the lungs are being filled with air, which if abdominal tensions allow, often occurs. 

3. Second stage of inhale would be to expand the ribs without straining.

4. Third stage of inhale is to allow the lungs to completely fill by raising the collar-bones (another good way to create UDB.) 

Throughout this procedure, the air should enter and exit from the mouth or nose in a continuous flow with no gasping.  No noise must be made for it is essential to breathe silently! It is of the utmost importance to concentrate the mind entirely upon the action of breathing!

When the lungs are completely filled, breathe out, in the same sequence as when inhaling ie; top of ribs, down to mid chest down to belly.

Now breathe in again in the same way. You may continue for as long as you wish. It should not induce any discomfort or fatigue. You can practice it at any time of day, whenever you think of it, at work, walking, any time; breathe consciously and as completely as possible.

Try it several times daily.  Breathe easily without straining. Remember that the ideal respiration is deep, slow, silent, easy.

The hope is that gradually you will acquire the habit of complete respiration, and your method of breathing will improve as you go on. Unfortunately this is not the case with many people. It DOES give many a sense of improvement and MAY even enhance breathing mechanics somewhat.  But my experience with this is that it heads many in the wrong direction for optimal breathing and develops blocks in future potential for natural breathing development and balance of the breathing driven Autonomic  Nervous System.

Let’s get the physiology right. 
Getting the physiology right means:

1. Helping practitioners to evolve their interventions based on facts, rather than on tradition, client feedback, and professional rumors,

2. Avoiding mixing effective factors with irrelevant ones, that take time, cost money, and side-track progress,

3. Avoiding unwitting introduction of counterproductive elements of training, such as deep breathing,

4. Avoiding faulty assumptions and misconceptions, about what is required for healthy breathing, such as the suppositions by many, that relaxation and slow breathing are necessarily prerequisite to good respiration, and

5. Providing high impact client/student, patient education, where both the perceived efficacy and credibility of breathing self-regulation are enhanced.

From a newsletter reader:

"I do breathing exercises (pranayama) but I want to know what I can do to make my breathing better. How can I make each breath longer, without having to think about my breathing? thanks!" 

From Mike: Get this program. www.breathing.com/video-ds.htm