Your mind is the natural environment for spiritual progress.
In order to keep the body and the mind healthy, the first step is to keep the digestive system in good condition.
Breath and mind are correlated. When the restlessness of the prana disappears, life becomes divine.
Entering the tongue in the nasal passage in pathway of the upper palate is called "the practice of Khechari Mudra." Although this is a physical technique of hatha yoga, it [brings about] a steady and still condition and is necessary to draw the mind inward. When this condition [the achievement of Khechari] happens, the sadhaka experiences somewhat more steadiness and stillness and becomes ready to advance to the second level of Kriya.