The Seven Principles of Systema Breathing
Inhale through nose; exhale through mouth.
Let breath slightly lead physical action in time.
Take as much breath as you need at the moment, for the action, not more not less.
Keep breathing, without interruption or holding, no matter what you are doing unless doing a special breath-hold training)
Let every breath cycle complete itself and reverse naturally, as a pendulum swings and reverses naturally without interference. Allow, and experience, the reversal pause at the end of each cycle.
No specific type of action is invariantly tied to any particular phase of breath cycle (i.e. you should be able to punch or roll as well on inhale as exhale).
7. No tension:
Keep your muscles and your body overall relaxed.