Attention plays a great part in concentration. It is the basis of will. The force with which anything strikes the mind is generally in proportion to the degree of attention bestowed on it. Attention on any object may be either subjective (internal) or objective (external). Practice concentrating your attention on unpleasant tasks, upon uninteresting objects and ideas. Then many mental weaknesses will vanish, and the mind will become stronger and stronger.
Sometimes the mind would refuse to put forth effort on account of inner Tamas (inertia) and lethargy. Don’t yield to this inertia. Remove it by constructive activity, study and Kirtan.
Remove slothness by being “Up and Doing.”