Nadi Shodana is a breathing practice with many benefits. This particular pranayama practice increases mental acuity and is helpful to do before tests or studying. It is named Nadi Shodana for it's ability to cleanse the energy centers through out the body, or nadis.
To begin, fold the first two fingers of your right hand into your palm. Use your thumb to close off the right nostril, as you breath into the left. When you start, take an inhalation to the count of five. If that makes you dizzy, reduce your count. (The longer you practice the more accustomed your body will become to deep breathing.) As soon as you reach the top of the inhalation, close the left nostril with your right ring finger, removing your thumb from the right nostril at the same time, and begin a slow, rhythmic, exhalation through this nostril. Do this to the count of five also. Inhale through the right nostril to the count of five. Close the right nostril with your right thumb. Exhale through the left nostril to the count of five. This is one round.
Practice 5 to 15 rounds and sit quietly for a moment soaking in the effects of your practice.