For yoga and meditation exercises I suggest only breathing in and out through the nose and try to extend the breathing for six seconds on the inhalation and six seconds on the exhalation. This allows us to expand the muscles in between each rib and actually get more oxygen into our lungs with every breath. The benefit of this kind of breathing is when there is a real emergency in your life you may not react with a panic attack or anxiety because you have practiced this kind of breathing with regularity. It helps with sleep and focus as well. This sort of long extended yoga breathing helped me when I was in a water explosion accident while driving. I was able to breathe my way slowly and safely to the freeway exit and not hit anybody and get myself to a gas station where I could pour cold water on my body.
I hope this helps.
Author and Creator of the Superior Self series