Divya nama sankeertana is the easiest method! Practice singing bhajans for half to one hour daily. Slowly it improves your concentration upon God and Guru.
Even Rishis are troubled by this problem of mental distractions. All human beings have this problem. It is part of God’s creation. It is only karma theory. So practice to sing the Lord’s name loudly. Then you will develop good concentration. Chanting the Lord’s names is the medicine for Kali yuga.
(Q&A Trinidad 19th July 2018)