Chanting should be performed with some feeling. Whether the emotion is hankering for Krishna, remorse, repentance, eagerness to chant more attentively, remembrance of our favorite pastime, or whatever, when there is some feeling, our chanting becomes less mechanical and more spontaneous. Try to capture these moments of chanting with feeling, and take note of what you were thinking about when the feeling came to you. Repeat your chanting in the same way and gradually the feeling will become more natural, and along with that will come a more natural desire to increase your chanting.
Collected Letters to Friends and disciples Vol 4, Pg 116, last paragraph.