When the mind is awfully restless and outgoing, we should tenaciously persist in our Japa, even do it mechanically, without giving in to this restlessness. That way, at least a part of our mind would be engaged in Japa. Thus the whole mind cannot become or remain restless.

Along with each repetition of the Name of your Istam (the Chosen Deity) or of your mantra (mystic sound symbol of the Divine), imagine that your whole body, mind and senses are becoming purified. This faith must be made firm, because in a way this is the idea underlying Japa. The Istam's Name soothes one's nerves, calms the mind and brings about helpful changes in the body. When the mind is in a state of great tension or depression, begin at once humming the Name and thinking of the Divine. Imagine that this is bringing about a balanced state, a new rhythm in the body and in the mind. Actually you will feel how it soothes the whole nervous system, how it stops the outgoing tendency of the mind more and more.

Reference: Meditation and Spiritual Life by Swami Yatiswarananda (p.412)​