Bhagavad Gita 6.12तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः।उपविश्यासने युञ्ज्याद्योगमात्मविशुद्धये ॥

The self means the mind. The real Supreme Self is the Atma. This is Primary (Mukhya). Mind also is the self. But this is used in a secondary sense (Gauna). Mukhya Atma is Brahman or the highest Self. Gauna Atma is the mind.Make the mind onepointed by collecting all its dissipated rays by the practice of Yoga. Withdraw it from all senseobjects again and again and try to fix it steadily on your Lakshya or point of meditation or centre. Gradually you will have concentration of the mind or onepointedness. You must be very regular in your practice. Only then will you succeed. Regularity is of paramount importance. You should know the ways and habits of the mind through daily introspection, selfanalysis or selfexamination. You should have a knowledge of the laws of the mind. Then it will be easy for you to check the wandering mind. When you sit for meditation, and when you deliberately attempt to forget the worldly objects, all sorts of worldly thoughts will crop up in your mind and disturb your meditation. You will be ite astonished. Old thoughts that you entertained several years ago, and old memories of past enjoyments will bubble up and force the mind to wander in all directions. You will find that the trapdoor of the vast subconscious mind is opened or the lid of the storehouse of thoughts within is lifted up and the thoughts gush out in a continous stream