Pranayama (Control of Breathing) : :
Unlike most os the works on Hathayoga, Maharishi Patanjali does not lay much stress of breath control. He recommends deep and slow regulated breathing as an aid to concentrated thought.
One should breath in deeply and hold the breath for few seconds and then slowly breath out again waiting for few seconds before drawing in again.
Perfection in slow, deep and rhythmic breathing gives one control over the senses, calms down the body and improves the level of concentration. It has to be practiced over a period of time regularly.