What are the classes of worship as per Bhakti yoga?

Bhakti Yoga has nine forms of worship called Nava-vidha Bhakti, which include listening to divine stories (Shravana), chanting the glories of God (Kirtana), meditating on God (Smarana), serving God's feet (Padasevana), worshiping the deity form of God (Archana), offering prayers to God (Vandana), serving God as a servant (Dasya), serving God as a friend (Sakhya), and surrendering oneself completely to God (Atma-nivedana).

“Four classes of pious people worship ,  people in distress, seekers of knowledge, seekers of material gain, and Knowers

The stages are:

1. Shraddha: faith in the words of Vaishnava Guru
2. Sadhu-sanga: association with Guru and Vaishnavas
3. Bhajan-Kriya: the actual practice of bhajan which is inspired by such association
4. Anarth-Nivritti: burning of majority of sins
5. Nishtha: unshakable determination in bhajan
6. Ruchi: natural interest springing in the mind to do bhajan. Rich food, clothes, wealth, all seem insipid or boring in comparison
7. Asakti: helpless attachment to Sri Radha Krsna. If a second of bhajan is lost, the devotee feels restless and begins to curse himself. Sheer addiction. The sadhak has to force himself to think about material matters, and even doing so for a second causes him pain.
8. Bhao: the preliminary stage of siddhi. The bliss of bhao bhakti is so epic and overwhelming, that the sadhak abandons Brahm-gyan, Shivatva, ashta-siddhis, etc. like trash. Sri Krsna begins showing glimpses of His divine Form. A great blazing fire of Viraha or separation burns within the heart of sadhak now. It swiftly burns remaining sin and tri-gun, tri-karm, tri-dosh, pancha-klesh, and pancha-kosh.
9. Prem: completion of sadhana. Radha Krsna give darshan. The devotee drowns in the infinite waves of Bliss that roll off from Their Body in the incarnations of sight, smell, sound, and touch. He repeatedly falls unconscious due to the bliss being infinite and too much.