Śrīla Jīva Gosvāmī Prabhu gives the following directions in his Bhakti-sandarbha (270):

iyaṁ ca kīrtanākhyā bhaktir bhagavato dravya-jāti-guṇa-kriyābhir dīna-janaika-viṣayāpāra-karuṇā-mayīti śruti-purāṇādi-viśrutiḥ. ata eva kalau svabhāvata evāti-dīneṣu lokeṣu āvirbhūya tān anāyāsenaiva tat-tad-yuga-gata-mahā-sādhanānāṁ sarvam eva phalaṁ dadānā sā kṛtārthayati. yata eva tayaiva kalau bhagavato viśeṣataś ca santoṣo bhavati.

“Chanting the holy name is the chief means of attaining love of Godhead. This chanting or devotional service does not depend on any paraphernalia, nor on one’s having taken birth in a good family. By humility and meekness one attracts the attention of Kṛṣṇa. That is the verdict of all the Vedas. Therefore if one becomes very humble and meek, he can easily attain the lotus feet of Kṛṣṇa in this Age of Kali. That is the fulfillment of all great sacrifices, penances and austerities because when one achieves ecstatic love of Godhead, he attains the complete perfection of life. Therefore whatever one does in executing devotional service must be accompanied by the chanting of the holy name of the Lord.” The chanting of the holy name of Kṛṣṇa — Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare — has been praised by Śrīla Rūpa Gosvāmī in his Nāmāṣṭaka (verse 1):

nikhila-śruti-mauli-ratna-mālā-
 dyuti-nīrājita-pāda-paṅkajānta
ayi mukta-kulair upāsyamānaṁ
 paritas tvāṁ hari-nāma saṁśrayāmi

“O Hari-nāma! The tips of the toes of Your lotus feet are constantly being worshiped by the glowing radiance emanating from the string of gems known as the Upaniṣads, the crown jewels of all the Vedas. You are eternally adored by liberated souls such as Nārada and Śukadeva. O Hari-nāma! I take complete shelter of You.”

Similarly, Śrīla Sanātana Gosvāmī has praised the chanting of the holy name as follows in his Bṛhad-bhāgavatāmṛta (part one, chapter One, verse 9):

jayati jayati nāmānanda-rūpaṁ murārer
 viramita-nija-dharma-dhyāna-pūjādi-yatnam
katham api sakṛd āttaṁ mukti-daṁ prāṇināṁ yat
 paramam amṛtam ekaṁ jīvanaṁ bhūṣaṇaṁ me

“All glories, all glories to the all-blissful holy name of Śrī Kṛṣṇa, which causes the devotee to give up all conventional religious duties, meditation and worship. When somehow or other uttered even once by a living entity, the holy name awards him liberation. The holy name of Kṛṣṇa is the highest nectar. It is my very life and my only treasure.”

In Śrīmad-Bhāgavatam (2.1.11) Śukadeva Gosvāmī says:

etan nirvidyamānānām icchatām akuto-bhayam
yogināṁ nṛpa nirṇītaṁ harer nāmānukīrtanam

“O King, constant chanting of the holy name of the Lord after the ways of the great authorities is the doubtless and fearless way of success for all, including those who are free from all material desires, those who are desirous of all material enjoyment, and those who are self-satisfied by dint of transcendental knowledge.”

In Śrīmad-Bhāgavatam (6.3.22) Yamarāja says:

etāvān eva loke ’smin puṁsāṁ dharmaḥ paraḥ smṛtaḥ
bhakti-yogo bhagavati tan-nāma-grahaṇādibhiḥ

“Devotional service, beginning with the chanting of the holy name of the Lord, is the ultimate religious principle for the living entity in human society.”

Similarly, Śrī Caitanya Mahāprabhu has said in His Śikṣāṣṭaka (3):

tṛṇād api su-nīcena taror iva sahiṣṇunā
amāninā māna-dena kīrtanīyaḥ sadā hariḥ

“One should chant the holy name of the Lord in a humble state of mind, thinking oneself lower than the straw in the street. One should be more tolerant than a tree, devoid of all sense of false prestige and ready to offer all respect to others. In such a state of mind one can chant the holy name of the Lord constantly.” Regarding the ten offenses in chanting the holy name, one may refer to Ādi-līlā, chapter eight, verse 24.