Surya Bhedana (piercing the sun) is a gentle warming/energising technique that involves inhaling through the right nostril and exhaling through the left.
The technique described here is for beginners and so does not include breath retention or bandhas.
All breathing is through the nose. Breathe as slowly as you comfortably can.
Technique
Get yourself into a comfortable sitting position with your back straight. Your right hand should be in prana mudra with the index and middle fingers folded inwards to touch the base of the thumb, and the third and small fingers together.
Bring the right hand up towards the nose. The tip of the thumb should rest gently against the right nostril, just where the bone meets the cartilage; and the tip of the third finger should rest gently against the left nostril, also just where the bone meets the cartilage.
Start with two full and complete inhalations and exhalations.
1/ Inhale again fully, and then close the right nostril with the tip of the thumb and exhale fully and completely through the left nostril.
2/ Close the left nostril and inhale slowly, fully, and completely through the right nostril.
3/ Close the right nostril and exhale slowly, fully and completely through the left nostril.
4/ Return to Step 2 and repeat the cycle.
Continue the cycle of inhaling through the right nostril and exhaling through the left nostril. When starting out, just do 2-3 minutes. But as you improve you can increase the time to 5-10 minutes.
Contraindications are the same as they are for Deep Breathing.