The correct process of receiving knowledge in any field is approaching a bona fide institute. Similarly, transcendental knowledge should be received through a bona fide disciplic succession
In Bhagavad Gita 4.2, Lord Krishna says:
imam rajarsayo viduh
sa kaleneha mahata
yogo nastah parantapa
Translation: “This supreme science was thus received through the chain of disciplic succession, and the saintly kings understood it in that way. But in course of time the succession was broken, and therefore the science as it is appears to be lost”
There are four sampradayas or authorities on the science of bhakti.
Sri Krishna Chaitanya is like a desire tree, and in the form of Narayana, He is the original guru of the four sampradayas.
(B) Lord Brahma is the leading disciple of the supreme Lord Narayana. His sampradaya is known as "Brahma Sampradaya" with disciples all over the world. In this sampradaya, Sri Madhva significantly contributed by writing a commentary on the Brahma-sutras. After this the sampradaya became known as the Madhva-sampradaya.
(C) The supreme Lord Narayana also has Lord Rudra as His disciple. Vishnusvami was a leading disciple in the "Rudra Sampradaya". Vishnusvami was very influential and a learned scholar of all the scriptures. After him this disciplic succession came to be known as the Vishnusvami-sampradaya.
(D) From the supreme Lord Narayana appeared the Hansa-avatara. In this disciplic succession came the four Kumaras headed by Sanaka Kumara. In this line Nimbaditya was a leading disciple in the "Kumara Sampradaya". The name Nimbaditya sampradaya was thus established.This is known also as Nimbarka-sampradaya. The influence of Nimbarka sampradaya spread all over the world.
The Sri, Brahma, Rudra, and Kumara sampradayas spread their influence by dividing into other sampradayas. In the Ramanuja-sampradaya, Sri Ramanandacharya was highly respected. He had many disciples and grand-disciples. Similarly Sri Vallabhacharya appeared in the Vishnusvami-sampradaya. He wrote a commentary named Anubhasya, which is highly respected. His disciplic succession is known as the Vallabha-sampradaya.
Iskcon Founder-Acarya His Divine Grace A.C. Bhaktivedanta Swami Prabhupada comes in the Brahma-Madhva-Gaudiya disciplic succession.
10. Jaya Tirtha
17. Brahmanya Tirtha
18. Vyasa Tirtha
20. Madhavendra Puri
21. Ishvara Puri, (Nityananda, Advaita)
22. Lord Chaitanya
23. Rupa Goswami, (Svarupa, Sanatana Goswami)
24. Raghunatha, Jiva Goswami
28. Srila Jagannatha Dasa Babaji Maharaja,(Srila Baladeva Vidyabhushana)
29. Srila Bhaktivinoda Thakura
30. Srila Gaurakishora Dasa Babaji Maharaja
31. Srila Bhaktisiddhanta Sarasvati Thakura
32. AC Bhaktivedanta Swami Prabhupada
Also read about the nine ways of doing bhakti as told by Prahalad Maharaj in Srimad Bhagavatam: