Diaphragm

As we breathe in, oxygen moves from atmosphere to lungs, to blood, and to cells of the body. As we breathe out, carbon dioxide returns from cells to blood, to lungs, and to atmosphere. The cells in the body take oxygen, generate energy, and give off carbon dioxide. 
Diaphragm is the main respiratory muscle in human body. It is a dome shaped structure and separates the chest cavity from the abdominal cavity. The heart and lungs rests on Diaphragm. As we take a deep breathe in and out, these organs get massaged by the diaphragm.

Breath Awareness

Come in the seated posture
Keep the spine and neck long
Place the hands on the thighs or knees
​Bring awareness to the breath; just noticing the breath without altering
Have a smooth transitions of breath, without pause and jerks

2:1 Breathing

Elongate the exhalation. Make it twice the inhalation
Use accessory breathing muscles to elongate the inhalation
Have a smooth transitions of breath, without pause and jerks
Example - Inhale for a count of 2 seconds; exhale for a count of 4 seconds

Diaphragmatic Breathing

Sit upright with elongated spine. Take a few natural breaths while placing hands on the upper abdomen just below the breast bone. Feel the rise and fall of belly with inhale and exhale. Inhale gently while holding just enough tension in the abdominal muscles. There's a feeling of expansion in the upper part of abdomen just below the sternum. The lateral excursion of rib cage is more pronounced which can be felt by placing the hands to the sides of the waist.

Alternate Nostril Breathing (Nadi Shodhana)

Curl the index and middle fingers of right hand in towards the palm
Close the right nostril with the thumb, inhale through the left nostril
Then, close the left nostril with the ring finger, exhale and inhale once through the right nostril
Again close the right nostril with the thumb, exhale and inhale once through the left nostril
Continue this process for 5 minutes
Benefits:
Best breathing exercise for calming the nervous system
Regulates blood pressure