Deep breathing is done while holding your breath' as well as inhaling and exhaling. Jaki wo haku-get rid or the bad energy(air) by forcing prolonged exhalation. Breath in the good air through the nose. Aim to breath only 2 to 5 times per min when relaxed. It's like a baby, you don't want to drop it but don't crush it either. Let it dance and sing. Flow from inhale to exhale to inhale as smoothly as possible. Obviously the more you breath from the tanden, the better. That means letting the belly rise when inhaling naturally and not breathing from the shoulders.
I have practiced different techniques of long inhale long exhale, short-long, long-short etc...
Also ways of holding breath and exerting energy in the various chakras, careful not to pass out. Reverse tanden breathing by pulling the belly in when inhaling which is also useful to eliminate sideburn when endurance runing.
j