Effective public communication comes from speaking only about topics you know intimately, in the same natural way you'd talk to a friend, rather than from traditional media-training techniques.
Marc Andreessen recounts his media trainer's core lesson: only speak on topics you know inside out, delivered as naturally as a lunch conversation with a friend, which became his lasting communication philosophy.
transcript
Marc Andreessen: He said, "If you are on stage or in an interview and you were talking about something and you don't know that topic inside out already, like what the hell are you doing there? So, the only thing that you should ever be talking about is something that you know you know intimately."