Diaphragmatic breathing is the most effective way to breathe. But many of the muscles that can produce pain referrals in the upper body are attached to the ribs. For this reason it is better to practice breathing using the belly and the chest to exercise all the muscles responsible for breathing.
Lie on your back with your knees bent. You can relax your legs by spreading the feet wide and letting the knee fall inward and lean against each other or you can place a pillow under the knees. Place one hand on the belly and one hand on the chest. Begin by inhaling into the belly using the diaphragm. The hand on the belly should rise up first. Then let the breath expand into the chest. Both hands should rise up equally but not necessarily at the same time. Try to breathe in for a count of three seconds if not longer. During the exhale allow both the chest and belly collapse expressing all the air. Let the exhale be as long out as the breath in. Toward the end of the breath pull the belly button into the spine pushing any remaining air out of the lungs.