In Bhakti-rasāmṛta-sindhu compiled by Śrī Rūpa Gosvāmī it is said that one should be very liberal in behavior and should avoid any undesirable activities. The most important affirmative points are that one should accept the shelter of a bona fide spiritual master, be initiated by him and serve him.
In addition to these, there are thirty-five items of devotional service, and they can be analyzed as follows: (1) hearing, (2) chanting, (3) remembering, (4) worshiping, (5) praying, (6) serving, (7) engaging as a servitor, (8) being friendly, (9) offering everything, (10) dancing before the Deity, (11) singing, (12) informing, (13) offering obeisances, (14) standing up to show respect to the devotees, (15) following a devotee when he gets up to go to the door, (16) entering the temple of the Lord, (17) circumambulating the temple of the Lord, (18) reading prayers, (19) vibrating hymns, (20) performing saṅkīrtana, or congregational chanting, (21) smelling the incense and flowers offered to the Deity, (22) accepting prasāda (food offered to Kṛṣṇa), (23) attending the ārātrika ceremony, (24) seeing the Deity, (25) offering palatable foodstuffs to the Lord, (26) meditating, (27) offering water to the tulasī tree, (28) offering respect to the Vaiṣṇavas or advanced devotees, (29) living in Mathurā or Vṛndāvana, (30) understanding Śrīmad-Bhāgavatam, (31) trying one's utmost to attain Kṛṣṇa, (32) expecting the mercy of Kṛṣṇa, (33) performing ceremonial functions with the devotees of Kṛṣṇa, (34) surrendering in all respects, (35) observing different ceremonial functions. To these thirty-five items, another four can be added: (1) marking one's body with sandalwood pulp to show that one is a Vaiṣṇava, (2) painting one's body with the holy names of the Lord, (3) covering one's body with the remnants of the Deity covers, (4) accepting caraṇāmṛta, the water which washes the Deity. These four additional items make thirty-nine items for devotional service in all, and out of all of these the following five are most important: (1) to associate with devotees, (2) to chant the holy name of the Lord, (3) to hear Śrīmad-Bhāgavatam, (4) to live in a holy place such as Mathurā or Vṛndāvana, (5) to serve the Deity with great devotion. These items are especially mentioned by Rūpa Gosvāmī in his book Bhakti-rasāmṛta-sindhu. The thirty-nine items above, plus these five items, total forty-four items. Add to these the twenty preliminary occupations and there are a total of sixty-four different items for conducting devotional service. One can adopt the sixty-four items with his body, mind and senses and thus gradually purify his devotional service. Some of the items are completely different, some are identical, and others appear to be mixed.
Śrīla Rūpa Gosvāmī has recommended that one live in the association of those who are of the same mentality; therefore it is necessary to form some association for Kṛṣṇa consciousness and live together for the cultivation of knowledge of Kṛṣṇa and devotional service. The most important item for living in that association is the mutual understanding of Bhagavad-gītā and Śrīmad-Bhāgavatam. When faith and devotion are developed, they become transformed into the worship of the Deity, chanting of the holy name and living in a holy place like Mathurā and Vṛndāvana.
The last five items—mentioned after the first thirty-nine—are very important and essential. If one can simply discharge these five items, he can be elevated to the highest perfectional stage, even if he does not execute them perfectly. One may be able to perform one item or many items, according to one's capacity, but it is the principal factor of complete attachment to devotional service that makes one advance on the path. There are many devotees in history who have attained perfection in devotional service simply by discharging the duties of one item, and there are many other devotees, like Mahārāja Ambarīṣa, who executed all the items. Some individual devotees who attained perfection in devotional service by executing only one item are: Mahārāja Parīkṣit, who was liberated and fully perfected simply by hearing; Śukadeva Gosvāmī, who became liberated and attained perfection in devotional service simply by chanting; Prahlāda Mahārāja, who attained perfection by remembering; Lakṣmī, who attained perfection by serving the lotus feet of the Lord; King Pṛthu, who attained perfection simply by worshiping; Akrūra, who attained perfection simply by praying; Hanumān, who attained perfection simply by becoming the servant of Lord Rāma; Arjuna, who attained perfection simply by being a friend of Kṛṣṇa's; and Bali Mahārāja who attained perfection simply by offering whatever he had in his possession. As far as Mahārāja Ambarīṣa is concerned, he actually performed all the items of devotional service. He first of all engaged his mind upon the lotus feet of Kṛṣṇa. He engaged his words, his power of speaking, in describing the transcendental qualities of the Supreme Personality of Godhead. He engaged his hands in washing the temple of the Deity, his ears in hearing the words of Kṛṣṇa and his eyes in beholding the Deity. He engaged his sense of touch by rendering service to the devotees, and he engaged his sense of smell by relishing the fragrance of the flowers offered to Kṛṣṇa. He engaged his tongue in tasting the tulasī leaves offered to the lotus feet of Kṛṣṇa, his legs in going to the temple of Kṛṣṇa, and his head in offering obeisances to the Deity of Kṛṣṇa. Because all his desires and ambitions were thus engaged in the devotional service of the Lord, Mahārāja Ambarīṣa is considered the leader in discharging devotional service in all kinds of ways.