When you need clarity, focus and more energy, try right nostril (Pingala) breathing.
Simply sit up straight, take your left hand and, with your fingers outstretched, block off your left nostril by putting gentle pressure on it with your left thumb. Inhale and exhale slow and deep through the right nostril. Do it continuously for 2-3 mins whenever you need the extra boost of energy. Visualize the sun and feel the sun energy flowing in your body, energizing every cell in your body.
Doing is believing.... Yogi Bhajan