As far as our ISKCON movement is concerned, we simply ask that one observe the four prohibitive rules, chant sixteen rounds and, instead of indulging in luxurious eating for the tongue, simply accept prasāda offered to the Lord. This does not mean that with our fasting the Lord should also fast. The Lord should be given foodstuff which is as nice as possible. But we should not make it a point to satisfy our own tongues. As far as possible we should accept simple foodstuff, just to keep the body and soul together to execute devotional service.
(Srimad Bhagavatam--4:8:72--purport).

In our Kṛṣṇa consciousness movement, we accept this principle by rejecting four prohibited items—namely illicit sex life, intoxication, gambling and flesh—eating—and accepting the daily chanting of at least sixteen rounds of the Hare Kṛṣṇa mahā-mantra and daily meditation three times a day by chanting the Gāyatrī mantra. In this way one can keep his brahminical culture and spiritual strength intact. By following these principles of devotional service strictly, chanting twenty-four hours a day the mahā-mantra—Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—one makes positive progress in spiritual life and ultimately becomes completely fit to see the Supreme Personality of Godhead face to face.
(Srimad Bhagavatam---4:21:42---purport).

To hear about Kṛṣṇa from Śrīmad-Bhāgavatam or Bhagavad-gītā or similar authentic literature is to live in Kṛṣṇa consciousness. Such concentration in Kṛṣṇa consciousness can be achieved by persons who are strictly following the rules and regulative principles. We have recommended in our Kṛṣṇa consciousness movement that a devotee chantsixteen rounds on beads daily and follow the regulative principles. That will help the devotee be fixed in his spiritual advancement in life.
Srimad Bhagavatam--4:22:24--purport).

In our preaching work also, we deal with so much property and money and so many books bought and sold, but because these dealings all pertain to the Kṛṣṇa consciousness movement, they should never be considered material. That one is absorbed in thoughts of such management does not mean that he is outside of Kṛṣṇa consciousness. If one rigidly observes the regulative principle of chanting sixteen rounds of the mahā-mantra every day, his dealings with the material world for the sake of spreading the Kṛṣṇa consciousness movement are not different from the spiritual cultivation of Kṛṣṇa consciousness.
(Srimad Bhagavatam--5:16:3--purport).

Certainly the chanting of 300,000 holy names of the Lord is wonderful. No ordinary person can chant so many names, nor should one artificially imitate Haridāsa Ṭhākura's behavior. It is essential, however, that everyone fulfill a specific vow to chant the Hare Kṛṣṇa mantra. Therefore we have prescribed in our Society that all our students must chant at least sixteen rounds daily. Such chanting must be offenseless in order to be of high quality. Mechanical chanting is not as powerful as chanting of the holy name without offenses.
(Sri Caitanya caritamrta--1:10:43--purport).

Haridāsa Ṭhākura used to chant the holy name on his beads 300,000 times daily. Throughout the entire day and night, he would chant the sixteen names of the Hare Kṛṣṇa mahā-mantra. One should not, however, imitate Haridāsa Ṭhākura, for no one else can chant the holy name 300,000 times a day. Such chanting is for the mukta-puruṣa, or liberated soul. We can follow his example, however, by chanting sixteen rounds of the Hare Kṛṣṇa mahā-mantra on beads every day and offering respect to the tulasī plant. This is not at all difficult for anyone, and the process of chanting the Hare Kṛṣṇa mahā-mantra with a vow before the tulasī plant has such great spiritual potency that simply by doing this one can become spiritually strong. Therefore we request the members of the Hare Kṛṣṇa movement to follow Haridāsa Ṭhākura's example rigidly. Chanting sixteen rounds does not take much time, nor is offering respects to the tulasī plant difficult. The process has immense spiritual potency. One should not miss this opportunity.
Sri Caitanya caritamrta---3:3:100---purport).