Establishing a seat in a clean environment that is not too high or too low, a yogi should cover his sitting place with kusha grass, a deerskin and a cloth. Sitting on that seat, fixing his mind on one point and controlling all the activities of the mind and senses, he should practice yoga to purify himself.
Bhagavad Gita - Chapter 6 - Dhyana Yoga - The Yoga of Meditation
Holding the body, head and neck straight, he should remain still and steady, gazing at the tip of the nose without casting his glance in other directions. Undisturbed, fearless and observing a vow of celibacy, he should sit and control his mind by thinking of Me as his highest goal.
In this way, the yogi controls his mind, withdrawing it from material desires. He then achieves supreme peace and liberation from material existence and attains My abode.
One cannot practice yoga by eating too much or too little, nor sleeping too much or too little, O Arjuna.
Yoga destroys the suffering of one who is moderate in eating and relaxation, who performs all activities in a regulated manner and is well balanced in sleeping and waking.
When the steady mind is fixed exclusively upon the self, then one becomes free from all material desires – such a person is said to be situated in yoga.
Just as a flame does not flicker in a windless place, similarly the mind of a yogi never wavers in its concentration on the self.
When the mind is restrained and peaceful by the practice of yoga, it becomes detached from material desires. Thus one can perceive the self and attain happiness. Being situated in this plane of eternal bliss, which is beyond the scope of the mundane senses and obtained through intelligence, one never deviates from reality. Upon gaining this position, one considers that there is nothing superior to this and does not become disturbed even in the midst of the greatest calamities. You should know that this state of being, wherein all miseries are destroyed, is known as yoga.
One should practice yoga with determination and an unwavering mind. In order to practice yoga, one must reject all thoughts that create material desires and withdraw the senses from the sense-objects using the mind.
Gradually, one should still the mind by means of the intelligence, focusing it on the self and nothing else.