Speaking or anything at all depends on practice and study. I remember when I was first asked to speak by one of my senior Godbrothers. I felt very much hesitating because I was not practiced to speak. Later on by speaking and hearing or reading I got experience, and now we can speak forty-five minutes, fifty minutes, or one hour at a stretch. So you have to read our books very nicely and gather thoughts, then you can speak for hours without any difficulty. It requires practice. So read our books carefully, especially Nectar of Devotion now published, and practice speaking. It will be all right.

(From Srila Prabhupada's letter to Upendra, June 24, 1970)