A really important message is delivered very succinctly in this 2 minute video. Although Alastair Campbell is talking about persuading people when speaking in public, his point is valid in pretty much any medium. 

He has two interrelated he points: First the message needs to be delivered by the author "For me, today, the only communication that works is real authenticity" further, " if someone is just reading a speech they were handed... it's never going to work".

Second, in order to persuade, a position should be founded on facts and framed by accessible experiences, to build a logical, relevant argument.