Hammer every thought in your mind thinking of how to serve Krishna.
The mind is not to be killed. Mind or desire cannot be stopped, but to develop a desire to function for spiritual realization, the quality of engagement by the mind has to be changed. The mind is the pivot of the active sense organs, and as susch if the quality of thinking, feeling and willing is changed, naturally the quality of actions by the instrumental senses will also change. — Srimad Bhagavatam, 02.01.17.
Keep your mind under captivity of remembering Lord Krishna.
You are where your mind is.
Unless one's mind is at least somewhat peaceful one cannot even begin to think about spiritual subjects.
Lecture on “Overcoming the IIT disadvantage” delivered at IIT Chennai on 19th Nov 2006