Our duty is simply to think about what would be most pleasing to Krsna. What is most pleasing to Krsna is to help others become Krsna conscious. The decision to preach because it is pleasing to Krsna is the best motivation. If we hold this favorable objective in our minds while sharing Krsna consciousness with others, then we cannot fail.
Lectures from a disciple Vol 1, pg 321, Bhaktyaloka, Moscow, 1.12.97