4. Ordinarily one breathes through the left nostril at the time of rest, through the right at the time of work, and through both at the time of meditation. The state most favorable to meditation is when the body and mind have become calm and there is even flow of breath through both nostrils. But do not pay too much atten�tion to watching your breath, nor make this a guide by which to regulate your activities.
5. When the mind is absolutely calm, breathing becomes steady and Kumbhaka (retention of breath) follows. When breath�ing is steady, the mind becomes one-pointed. Bhakti (love of God) also brings about Kumbhaka without effort, and breathing becomes steady. Even without practicing Yoga, Pranayama (control of breath) is attained automatically if one remembers and thinks of the Lord and does Japa with a yearning heart.
6. There is no other easy or convenient method to achieve one-pointed ness of mind except by Abhyasa, or repeated and sustained efforts, and by Vairagya, or non-attach�ment to worldly objects.
Source: Parmarth Prasanga -Towards The Goal Supreme- Swami Virajanandaji of Ramakrishna Math