In Bhajana Rahasya, Srimad Bhaktivinode Thakur explains the following verse from Sri Sanatana Goswami’s Haribhakti-vilasa:
manah samharanam saucam maunam manträrtha-cintanam
avyagratvam anirvedo japa – sampatti – hetavah
The Thakur says that this instruction applies to both nama-japa and mantra-japa (a.k.a “gayatri”). The advice here is: “Take complete control of your thoughts, making them pure and silent. Contemplate the meaning and intention of the mantra. Be resolute, but patient – then you will bring about the full realization of chanting.”
The Thakur elaborates on mantrartha-cintana (“contemplating the meaning and intention of the mantra“) with five specific instructions:
1) Educate yourself in the meaning of the mantra, and the on the persons named by the mantra. In other words, learn the various multifaceted meanings of the words “hare, krishna, rama” and learn the qualities, form, and pastimes of the persons named by those words.
2) Consider the person(s) named in the mantra to be your only true protector, and chant the mantra many times (instead of just once) for their pleasure.
3) Consider that there is nothing existing at all outside of the mantra. The mantra, being non-different from the divine beings it names, encompases all of reality.
4) Give yourself to the mantra in the mood of needing to be rescued by it.
5) Give your heart and soul to the mantra. If chanting it conflicts with other interests, sacrifice those interests. Sacrifice everything for the mantra, but never sacrifice the mantra for anything.
Bhaktivinode Thakur says that if we chant in this manner, we will attain astonishing results extremely rapidly.