Mantra is an extraordinary practice. However, at some point, mantra flows naturally, so it becomes a part of the being rather than a practice. Mantra is the most effective when it is initiated by the Satguru. Then the word becomes a "piece" of the guru, a holy word that may bring one all the way to realization of one's True Nature. There are many spiritual aspirants that have chanted the holy name until all karma is burned in the Fire. Valmiki was one sage who received the holy name, Ram, from Sage Narada. He chanted Ram constantly until he became enlightened, and then he wrote the Ramayana, one of the most influential literary works in all of history. This is the result of mantra.
One may chant a mantra so often that it chants silently by itself inside the Heart. A mantra invokes the gods that within us. Gods represent energy such as love, peace, and joy. Here is the mahamantra:
Hare Krishna Hare Krishna
Krishna Krishna Hare Hare
Hare Rama Hare Rama
Rama Rama Hare Hare
This one is known throughout the world. When invoked with the blessing of the Guru, it invokes Krishna, the Supreme Presence, to bring us to Him. It assists a person in dissolving into the Cosmic Presence that is beyond the mind. It is not possible to understand. As I feel the energy of the mantra, I become more devoted to it. When blocks such as boredom or frustration come up, I let them go and re-connect to the energy. Chanting the mantra with love, humility, joy, and peace is the best way to connect. It can be fun to read the amazing stories of Krishna in the Srimad Bhagavatam to increase one's devotion to Krishna, and therefore, one may connect more deeply to the mantra.
I bow down to the Holy Word of the Guru, that which brings me across the ocean of suffering. May the Holy Name heal all beings in this world.