Chanting a mantra or hymn softly and slowly is called japa, and chanting the same mantra loudly is called kīrtana. For example, uttering the mahā-mantra (Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare) very softly, only for one's own hearing, is called japa. Chanting the same mantra loudly for being heard by all others is called kīrtana. The mahā-mantra can be used for japa and kīrtana also. When japa is practiced it is for the personal benefit of the chanter, but when kīrtana is performed it is for the benefit of all others who may hear.
(Nectar of Devotion).

In the Nāradīya Purāṇa it is directed, "One should not accept more than necessary if he is serious about discharging devotional service." The purport is that one should not neglect following the principles of devotional service, nor should one accept the rulings of devotional service which are more than what he can easily perform. For example, it may be said that one should chant the Hare Kṛṣṇa mantra at least one hundred thousand times daily on his beads. But if this is not possible, then one must minimize his chanting according to his own capacity. Generally, we recommend our disciples to chant at least sixteen rounds on their japa beads daily, and this should be completed. But if one is not even able to chant sixteen rounds, then he must make it up the next day. He must be sure to keep his vow. If he does not strictly follow this out, then he is sure to be negligent. That is offensive in the service of the Lord. If we encourage offenses, we shall not be able to make progress in devotional service. It is better if one fixes up a regulative principle according to his own ability and then follows that vow without fail. That will make him advanced in spiritual life.
(Nectar of Devotion).

As already explained, one should not be idle but should be very enthusiastic about executing the regulative principles—tat-tat-karma-pravartana. Neglect of the regulative principles will destroy devotional service. In this Kṛṣṇa consciousness movement there are four basic regulative principles, forbidding illicit sex, meat-eating, gambling and intoxication. A devotee must be very enthusiastic about following these principles. If he becomes slack in following any of them, his progress will certainly be checked. Śrīla Rūpa Gosvāmī therefore recommends, tat-tat-karma-pravartanāt: "One must strictly follow the regulative principles of vaidhī bhakti." In addition to these four prohibitions (yama), there are positive regulative principles (niyama), such as the daily chanting of sixteen rounds on japa-mālā beads. These regulative activities must be faithfully performed with enthusiasm. This is called tat-tat-karma-pravartana, or varied engagement in devotional service.
(Nectar of Instruction).

In this Kṛṣṇa consciousness movement a chance is given to everyone without discrimination of caste, creed or color. Everyone is invited to join this movement, sit with us, take prasāda and hear about Kṛṣṇa. When we see that someone is actually interested in Kṛṣṇa consciousness and wants to be initiated, we accept him as a disciple for the chanting of the holy name of the Lord. When a neophyte devotee is actually initiated and engaged in devotional service by the orders of the spiritual master, he should be accepted immediately as a bona fide Vaiṣṇava, and obeisances should be offered unto him. Out of many such Vaiṣṇavas, one may be found to be very seriously engaged in the service of the Lord and strictly following all the regulative principles, chanting the prescribed number of rounds on japa beads and always thinking of how to expand the Kṛṣṇa consciousness movement. Such a Vaiṣṇava should be accepted as an uttama-adhikārī, a highly advanced devotee, and his association should always be sought.
(Nectar of Instruction).

"One whose faith is soft and pliable is called a neophyte, but by gradually following the process, he will rise to the platform of a first-class devotee." Everyone begins his devotional life from the neophyte stage, but if one properly finishes chanting the prescribed number of rounds of hari-nāma, he is elevated step by step to the highest platform, uttama-adhikārī. The Kṛṣṇa consciousness movement prescribes sixteen rounds daily because people in the Western countries cannot concentrate for long periods while chanting on beads. Therefore the minimum number of rounds is prescribed. However, Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura used to say that unless one chants at least sixty-four rounds of japa(one hundred thousand names), he is considered fallen (patita). According to his calculation, practically every one of us is fallen, but because we are trying to serve the Supreme Lord with all seriousness and without duplicity, we can expect the mercy of Lord Śrī Caitanya Mahāprabhu, who is famous as patita-pāvana, the deliverer of the fallen.
(Nectar of Instruction).