Most people, as they walk around in their daily lives, inhale into their upper lungs i.e., their shoulders go up as does their chest. When the air is in your upper lungs, you don't have the kind of detailed control you need. A singer (or a swimmer or runner--anyone who has to control their air) should fill their lower lungs. This means that instead of a breath that is vertical, with your body expanding upwards, the breath should be horizontal, expanding outwards.
Put one hand on your abdomen and the other hand on your back, both at about waist level. Inhale by filling your lower lungs with air so that your stomach sticks out. Your hands should move apart, the air filling the space between them. As you exhale let your stomach go back in gently. Think of your stomach as a balloon that inflates and deflates. Your chest shouldn't move, not even an eighth of an inch. As you get better at this, your back will also move out when you inhale. Try putting your thumbs one on each side of your spine, at about waist level. Relax your shoulders. Now inhale into your thumbs.
Once you put the air in the right place, you must learn to control it with your diaphragm. The diaphragm is a muscle that sits below your lungs and causes them to fill and empty. If you exhale out all of your air down to the absolutely last drop, you will feel your diaphragm under your rib cage as it pushes up against your lungs. On the outside of your ribs you will feel your abdominal wall pushing in; inside your ribs your diaphragm pushes up. Not only does your diaphragm need to be strong enough to push hard when you want lots of power, but it needs to have even more control and strength when you want to sing a fast and accurate lick, or a big jump in pitch, or very, very quietly. Building the strength and control of your diaphragm begins with proper breathing.
To strengthen the diaphragm, again put one hand on your abdomen and the other hand on your back. Inhale into your abdomen and exhale forcibly so that your stomach muscles push in and the air comes out rapidly. Repeat this--inhale, abdomen out, exhale forcibly, abdomen in--thirty times picking up the tempo as you get comfortable with it. Breathe through your mouth. As you go faster you may find that you've fallen back into the old habit of breathing vertically again. In that case, stop and start over by breathing slowly and gently into your lower lungs until you have the feeling again.
Initially you may feel that you can't get enough air, but that is because your lung capacity is small from disuse. All infants breath into their lower lungs, but as we age and our stress levels increase, our breathing tends to move upwards. With practice you will find that your lower lungs stretch out and that your ribs in the back will loosen up and make room for the larger inhalation.
Be patient with yourself. After breathing vertically thousands of times a day all the years of your life, a new way to breathe takes lots of concentration. Remember that your voice is an instrument like any other. It takes time to learn to play it--time and patience and practice.
Copyright 1990 by Lis Lewis, used with permission. The Lis Lewis Singers' Workshop, has clients at RCA, CBS, and Warner Bros. and many more.