Contract your abdominal muscles, forcefully, creating an exhale, by pumping your stomach muscles in and out, hard and fast, but controlled. Air will enter the top part of your lungs by itself. Use the rapid contractions of your abdominal muscles to inhale and exhale with this exercise. The contractions should be rhythmic.Practice a few times, and get a feel for it.
Do 20 in a row, in and out, using your abdominal muscles in rapid succession, and at the end of the 20th breath, exhale, inhale and fill your lungs, contract your anus, lower your chin to your chest, hold your breath as long as you comfortably can. Exhale slowly.
The above constitutes one round. The exhalation should be brief, and the inhalation should be passive and longer. Rounds are increased by adding the number of pumpings with your abdominal muscles. First, try doing three sets of 20 pumpings and then after some time, increase to 30, then 40 until you are doing 60.