Pranav Pranayama is mostly practiced for spiritual development and is the zenith in Pranayama. This helps us in controlling the mind. It urges us to feel the presence of god within us, outside us and all around us. Being completely and totally immersed in the vision of God is what Pranav Pranayama is all about. Therefore this is the Pranayama that helps us to concentrate.
Here is what you need to do to perform this Pranayama. Close your eyes and sit silently. Concentrate deeply in breathe in and out and focus on the vision of God. Feel God in every particle in your body and meditate deeply. The deeper you mediate the more spiritually blessed you will be. Even though this Pranav Pranayama just requires one to breathe in and out normally for 2-3 minutes every day, it is considered to be the most cleansing since it helps generate a spiritual blanket around us and keeps our mind fresh and open.
Pranava Pranayama is all about submitting ourselves to the divine powers above and relying completely on the power of the divine chanting Om, pronounced as Aum. You need not necessarily sit in the altar in your home or go to a temple to feel connected to God. God is wherever you want him to be and his blessings are best felt inside us. So the next time you feel the need to reach out to Him, just sit comfortable, close your eyes, breathe in and out and you will find God right beside you. All the while you will also be healing your body with all sorts of impurities and negative vibes.