While in meditatiion how should we breathe? Should air fill chest or go to belly first and then gradually expand the chest. Please guide
Your breathing, while you are meditating, will vary according to which meditation or pranayam technique you are practicing.
If you are practicing Yogananda’s Hong-Sau technique, the focus is on breathing naturally, not controling the breath in any way, and observing the breath until it slows down and becomes very calm, almost unmoving — thus bringing your mind also into a very calm state.
If you are practicing Kriya Yoga, then there is another breathing technique involved, which I can’t described here, as it involves your becoming a disciple of this path first and taking Kriya Yoga Initiation.
What it sounds like you are describing in your question is “belly breathing” or Full Diaphragmatic Breathing, which is often taught as a part of Hatha Yoga. It is a wonderful de-stressing or relaxing technique, but it is generally not used for silent, sitting meditation.
If you would like to learn more about the techniques of Paramhansa Yogananda’s path of Kriya Yoga, please go to one or both of these sections of Ananda’s website: