You must have a pure mind if you want to realise the self. Unless the mind is free and it casts away all desires, cravings, worries, delusion, pride, lust, attachment, likes and dislikes, it cannot enter into the domain of supreme peace and unalloyed felicity, the immortal abode.
A glutton or a sensualist, a dullard or a lazy man, cannot practise meditation. He who has controlled the tongue and other organs, who has an acute acumen, who eats, drinks and sleeps in moderation, who has destroyed selfishness, lust, greed and anger, can practise meditation and attain success in samadhi (superconsciousness).
You cannot enjoy peace of mind, you cannot practise meditation if there is viksepa in your mind. Viksepa is tossing of mind. Viksepa is rajas (passion); viksepa and desires co-exist in the mind. If you really want to destroy viksepa, you must destroy all mundane cravings through dispassion and self-surrender to the Lord.
If you apply fire to green wood, it will not burn; if you apply fire to a piece of dried wood, it will at once catch fire and burn. Even so, those who have not purified their minds will not be able to start the fire of meditation. They will be sleeping or dreaming building castles in the air - when they sit for meditation.
But those who have removed the impurities of the mind by japa (repetition of God's name), service, charity, pranayama (yoga breathing) etc., will enter into deep meditation as soon as they sit for meditation. The pure ripe mind will at once burn with the fire of meditation.
Clarify your idea again and again. Think clearly. Have deep concentration and right thinking. Introspect in solitude. Purify your thoughts. Still the thoughts. Silence the bubbling mind. Allow one thought-wave only to rise from the mind and settle down calmly. Then allow another thought to enter. Drive off all extraneous thoughts that have nothing to do with the subject matter on hand. An efficient control over thoughts, through long practice, is a great help in meditation.
Watch every thought very carefully. Shut out all useless thoughts from the mind. Your life must tally with your meditation. You keep up your meditation during work also. Do not give new strength to evil thoughts by constantly thinking. Restrain them. Substitute sublime thoughts.