Hi Miguel,
This is the way I've been taught to do it (from Saddguru Jaggi Vasudev, you can watch some videos of him on Youtube if you like)
sit in siddhasana, spine erect (no need to stimulate the muladhara, just sit in a comfortable way)
- your left hand, palm facing upward, rests just above your genitals, or let's say gently resting on them.
-your right hand, fingers straight, pointing upward, in front of your nose
-the 2 fingers you use are the thumb and the little finger
- start by exhaling veeeeeeery slowly from the left nostril, thumb is closing the right nostril
- after exhaling fully, you start inhaling very slowly
- as soon as you finish inhaling fully,close the left nostril with the little finger and open the right nostril; exhale very slowly from the right nostril.(this is half a round)
- then, inhale very slowly from the right nostril
- close the right nostril with the thumb, and exhale through left nostril (this makes 1 complete round)
So after each inhalation, you change the nostril.
No counting, no breath hold, just slow inhale and exhale from left to right, right to left..
This is a powerful technique for balancing ida and pingala.
It is very relaxing for the brain..
Experiment with it and see how it feels.
I can't say how much time you need to do it..
It can be done from 2 minutes to 1 or more hours..
important note: shoulders and arms are relaxed and the head should remain straight. Also the breathing should be done as slowly as possible, but without forcing to the point of tension or discomfort.
Just relax into it and slowly feel the air coming in and out.
Don't visualize anything.. just feel.
Love