By Swami Sivananda
This tatamounts to mediation on OM. You can take one of the Mahavakhyas*, for example, "Aham Brahma Asmi" (I am Brahman) and meditate on its meaning. Negate the Koshas (5 five sheaths, physical, praniic, mental, intellectual, causal) and identify yourself with the one essence that lies behind them, (Atman, Consciousness).
When you repeat mentally: "Aham Brahma Asmi." Lip repetition will not produce much benefit. You must intensely feel from the subjective heart. Gradually, you will be taken to superconscious state through deep feeling.
Sit in your Asana on a fourfold blanket. Face North or East and Constantly feel that you are the pure (Suddha), All-Pervading (Vyapaka), Sat-Chit-Ananda* Atman.
1. Infinity I am.
2. Eternity I am.
3. Immortality I am.
Meditate. Purify your mind. Practice concentration in a solitary room.
Unfold the Divinity that is lurking in your heart by concentration and meditation. Do not waste your time. Do not waste your life.
Meditate. Meditate. Do not waste even a single minute. Meditation will eliminate the miseries of life. Meditation is the enemy of the mind. Will bring the death of the mind (Manonasha).
~ Swami Sivananda
*SAT-CHIT- ANANDA means: (Existence Absolute, Knowledge Absolute, Bliss Absolute,).
The Mahavakyas (singular: Mahavakya, महावाक्य; plural: mahāvākyāni, महावाक्यानि) are "big words" of the Upanishads, the foundational texts of Vedanta.
The four Upanishadic statements indicate the last unit of the individual (Atman) with the Supreme (Brahman).
The Mahavakyas are:
~ Prajnanam brahma - "Consciousness is Brahman" (3.3 Aitareya Upanishad of the Rig Veda)
Ayam atma brahma "This Self (Atman) is Brahma" (Mandukya Upanishad 1.2 of Atharva Veda)
~ Tattvamasi - "Thou art That" (Chandogya Upanishad 6.8.7 of Sama Veda)
Aham Brahmasmi ~ - "I am Brahman" (Brhadaranyaka Upanishad 1.4.10 of the Yajur Veda)