Nadi Shodhana
Two ways to perform this exercise:
From a seated position,
1. Exhale through both nostrils. With only your awareness attempt to inhale only through your right, then out your left, then in your left, and out the right. This completes one cycle.

Or if you are having trouble isolating the nostrils,

2. Left hand, touch the tip of your thumb and index finger together. Extend the other 3 fingers. Rest the back of the hand on the knee. Right hand, bring the tip of the index and middle fingers to the base of the thumb. Bring the ring and pinkie fingers together. Use the thumb and middle fingers to control the nostrils. Exhale through both nostrils. Close the left, inhale through the right, close the right, exhale through the left. So on and so forth.