In this wonderful video, you can watch the rhythmic movements of every breath we take. The biomechanics of breathing are crucial to understand, to improve an freeing up the breath. 

Basically optimal breathing is about space, elasticity and rhythm. If you are too tight and locked into a ribcage, spine, abdomen and pelvis that cannot move an synchronize every breath - breathing is a "fight". 

So, working with all of the tissue surrounding and co-working with the lungs and diaphragm, are the first priority to work with. Both being able to use your nose and your 3-dimensional breath - designed by nature.