Lord Krishna instructs Uddhava on how He can be attained

SB 11.12.12: My dear Uddhava, just as great sages in yoga trance merge into self-realization, like rivers merging into the ocean, and are thus not aware of material names and forms, similarly, the gopīs of Vṛndāvana were so completely attached to Me within their minds that they could not think of their own bodies, or of this world, or of their future lives. Their entire consciousness was simply bound up in Me.

SB 11.12.13: All those hundreds of thousands of gopīs, understanding Me to be their most charming lover and ardently desiring Me in that way, were unaware of My actual position. Yet by intimately associating with Me, the gopīs attained Me, the Supreme Absolute Truth.

SB 11.12.14-15: Therefore, My dear Uddhava, abandon the Vedic mantras as well as the procedures of supplementary Vedic literatures and their positive and negative injunctions. Disregard that which has been heard and that which is to be heard. Simply take shelter of Me alone, for I am the Supreme Personality of Godhead, situated within the heart of all conditioned souls. Take shelter of Me wholeheartedly, and by My grace be free from fear in all circumstances.

Simply by association with Me and My devotees, they achieved Me.

SB 11.12.1-2: The Supreme Personality of Godhead said: My dear Uddhava, by associating with My pure devotees one can destroy one's attachment for all objects of material sense gratification. Such purifying association brings Me under the control of My devotee. One may perform the aṣṭāńga-yoga system, engage in philosophical analysis of the elements of material nature, practice nonviolence and other ordinary principles of piety, chant the Vedas, perform penances, take to the renounced order of life, execute sacrificial performances and dig wells, plant trees and perform other public welfare activities, give in charity, carry out severe vows, worship the demigods, chant confidential mantras, visit holy places or accept major and minor disciplinary injunctions, but even by performing such activities one does not bring Me under his control.

SB 11.12.3-6: In every yuga many living entities entangled in the modes of passion and ignorance gained the association of My devotees. Thus, such living entities as the Daityas, Rākṣasas, birds, beasts, Gandharvas, Apsarās, Nāgas, Siddhas, Cāraṇas, Guhyakas and Vidyādharas, as well as such lower-class human beings as the vaiśyas, śūdras, women and others, were able to achieve My supreme abode. Vṛtrāsura, Prahlāda Mahārāja and others like them also achieved My abode by association with My devotees, as did personalities such as Vṛṣaparvā, Bali Mahārāja, Bāṇāsura, Maya, Vibhīṣaṇa, Sugrīva, Hanumān, Jāmbavān, Gajendra, Jaṭāyu, Tulādhāra, Dharma-vyādha, Kubjā, the gopīs in Vṛndāvana and the wives of the brāhmaṇas who were performing sacrifice.

SB 11.12.7: The persons I have mentioned did not undergo serious studies of the Vedic literature, nor did they worship great saintly persons, nor did they execute severe vows or austerities. Simply by association with Me and My devotees, they achieved Me.

Lord Krishna's words on relationship between Guru and Disciple

SB 11.10.12: The spiritual master can be compared to the lower kindling stick, the disciple to the upper kindling stick, and the instruction given by the guru to the third stick placed in between. The transcendental knowledge communicated from guru to disciple is compared to the fire arising from the contact of these, which burns the darkness of ignorance to ashes, bringing great happiness both to guru and disciple.

SB 11.10.13: By submissively hearing from an expert spiritual master, the expert disciple develops pure knowledge, which repels the onslaught of material illusion arising from the three modes of material nature. Finally this pure knowledge itself ceases, just as fire ceases when the stock of fuel has been consumed.

Lord Krishna's instruction on having a Spiritual Master

SB 11.10.5: One who has accepted Me as the supreme goal of life should strictly observe the scriptural injunctions forbidding sinful activities and, as far as possible, should execute the injunctions prescribing minor regulative duties such as cleanliness. Ultimately, however, one should approach a bona fide spiritual master who is full in knowledge of Me as I am, who is peaceful, and who by spiritual elevation is not different from Me.

SB 11.10.6: The servant or disciple of the spiritual master should be free from false prestige, never considering himself to be the doer. He should be active and never lazy and should give up all sense of proprietorship over the objects of the senses, including his wife, children, home and society. He should be endowed with feelings of loving friendship toward the spiritual master and should never become deviated or bewildered. The servant or disciple should always desire advancement in spiritual understanding, should not envy anyone and should always avoid useless conversation.