Preaching does not mean pointing out others’ faults and shortcomings. That isn’t preaching, but faultfinding. Preaching means to encourage the spark of Krishna consciousness in others, and maintaining faith that the development of Krishna consciousness will automatically eliminate any bad qualities they may have. The Bhagavatam states, yasyasti bhaktir bhagavaty akincana, devotees develop all good qualities.
Lectures from a disciple Vol 1, Pg 72, 4th Paragraph