Okay, so there are 2 different methods of breathing used in psionics. Normal and Reverse. Here I shall detail them.
This is when you breath fully, while moving your ribs as little as possible. So don't fill your lungs 100%, but fill them up until it's unnatural to breath further. Then, exhale the same way (until it's unnatural to empty your lungs further). The amounts should be 80% and 10%, respectively. This is used to store more Ki in your body.
This is when you do the opposite of Normal Breathing, which is breathe 10% in and 80% out. This compresses your Ki into Jing, which is an energy we use constantly in everyday life to do physical activities (such as walking). When we are in extreme danger, our bodies automatically Reverse Breath to ready us for necessary self defense.