How to achieve concentration of mind? – Swami Sivananda

Make the mind one-pointed by collecting all the dissipated rays of the mind. Withdraw the mind from all sense-objects again and again and try to fix the mind on your Lakshya or point of meditation or center. Gradually you will have concentration of mind or one-pointedness. You must be patient and persevering. You must be very regular in your practice. Then only you will succeed. Regularity is of paramount importance.

Swami Sivananda