Constant engagement in devotional service can be performed only when one is working under the direction of a bona fide spiritual master. The Vedic injunction is that no one can have full knowledge without being under the guidance of an Acarya.
If after accepting the spiritual master and being initiated one does not follow the rules and regulations of devotional service, then he is again fallen.
One must execute devotional service under the guidance of a devotee or directly under the guidance of the Supreme Personality of Godhead. It is not possible, however, to train oneself without guidance from the spiritual master.
By the slow process of devotional service, under the guidance of the bona fide spiritual master, one can attain the highest stage.
One must seek the association of persons who are Krishna Conscious and who engage in devotional service. Without such association one cannot make advancement.
In the association of pure devotees, discussion of the pastimes and activities of the Supreme Personality of Godhead is very pleasing and satisfying to the ear and the heart. By cultivating such knowledge one gradually becomes advanced on the path of liberation and thereafter he is freed and his attraction becomes fixed. Then real devotion and devotional service begin.