When is one able to talk about Krishna Consciousness to others? What are the qualifications needed? In the Nectar of Devotion we read about the three classes of devotees, but only the first class devotee is able to preach? Or is the difference that the first-class devotee is able to present more arguments while the others should only speak about direct instructions?

Ask yourself a practical question: if I speak to this or that person, will that person have a better life? If yes, then we should speak.