Soften the Belly
When breathing, the diaphragm should be relaxed enough that your abdominal wall rises and falls with the breath. Your belly should expand and fill when you inhale, and empty completely when you exhale. If you are an athlete, with a muscular stomach, give yourself time and practice when learning how to relax this vital area. Diagnose Imbalances
It is ideal if the length of both inhale and exhale are approximately the same. As you pay attention to your breathing, you may first find that your belly is not moving. Correct this by practicing softening, relaxing, and stretching the abdominal wall, in addition to allowing long relaxed breaths, both in and out. As your breath becomes balanced, your mind becomes balanced. As your deep breath becomes a way of being, your body and mind becomes robust and serene at the same time. Stretching and Bodywork
People often have difficulty breathing deeply because the back muscles and intercostals (around and between the ribs) are too tight. Stress, lack of exercise, too much exercise, or bodily held feelings often cause the muscle groups around torso to restrict the movement of the rib cage. As stress and holding dissolves, the breathing parts (belly, diaphragm, ribs, lungs, and back) can move in an easier way. The diaphragm opens more. The chest and back muscles soften, creating more ease for the rising and falling of the ribs. Stretching, stress reduction, meditation, bodywork, general relaxation, and emotional release all contribute toward dissolving body armor and making the body more open. Practice Breath Awareness
It is not likely that you will always be aware of your breathing. Therefore, I suggest that you set aside times to practice and focus upon the breath. I like to practice slow deep breathing when I am working at the computer, when driving on long stretches of open road, when giving bodywork, and as a way to begin meditation. It tends to foster a relaxed, focused state of mind. Take long deep breaths, both in and out, relax the belly, breathe, flow, and go. My meditation always begins with a few moments of being mindful of the breath. The breath can also be used to open the heart. In Tonglen Buddhist meditation, you practice breathing in the suffering of all beings around you. On the exhale you release and send any happiness or joy you have. Or, you can contemplate all the dualities of life. Breathe in, life is born. Breathe out, life dies. Breathe in, day. Breathe out, night. Breathe in, yin. Breathe out, yang.
Breathing is so basic. It is one of the easiest things to miss. And that is also how our essential nature is: basic, natural. But, we have habits of complicating this. Then we spend years trying to shed our complications. However and whenever you consciously breathe, do it with awareness, an attitude of good health, and a love for yourself, and all of life.
Sara's Note: I found this article on About.com: http://healing.about.com/od/breathwork/a/consciousbreath.htm