Diaphragmatic- Abdominal Breathing
I have found it very helpful to breathe in this particular way, which involves relaxing the belly. It may or may not be the way you are already breathing. " In abdominal breathing or diaphragmatic breathing, the idea is to relax your belly as much as you can. Then, as the breath comes in, the belly expands slightly (on its own) in an outward direction as the diaphragm pushes down on the content of the abdomen from above. The diaphragm can go down farther when this happens so the in breath is a little longer and lungs fill with a little more air Then a little more air is expelled on the out breath, so that, overall, the full cycle of your breathing will be slower and deeper."
Jon Kabat-Zinn, Full Catastrophe Living