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.
To practice the deeper form of breathing, start by lying on your back with your knees bent. You can relax your legs by spreading your feet wide and letting your knee fall inward and lean against each other or you can place a pillow under the knees. Place one hand on your belly and the other hand on your chest. Begin by inhaling into your belly using the diaphragm. The hand on your belly should rise up first. Then let your breath expand into your 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 your chest and belly collapse expressing all the air. Let your exhale be as long out as the breath in. Toward the end of your breath pull your belly button into the spine pushing any remaining air out of your lungs.