The way to realise is through a quiet mind and a vital free from desires. To reject the desires and demands of the vital and to quiet the excessive activity of the mind, so that a true consciousness and spiritual perception and knowledge may take the place of the mind’s activity, are the requisite conditions of the Yoga.
The further method is,—(1) To concentrate in the heart and aspire and (2) to call to the divine Mother to enter there and purify the mind and vital and unveil the psychic being so that her constant guidance and presence in it may be felt always and (3) to concentrate in the quiet mind and (in the head) open oneself first to the divine force and light which is always above the mind and call to it to descend into the body and the whole being—either of these or both, according to the capacity of the sadhaka.
Yoga must be done not for oneself or what one can get but for the sake of the Divine and to be united with the Divine.
If he can do any of these things (not minding how long it takes) in this spirit, then let him do Yoga; if he cannot, then there is no use in doing it.
Ref: Letters on Yoga – II