‘One: tell them what you’re going to tell them; two: tell them; three: tell them what you just told them.’ It’s the first lesson of public speaking and debating and is a formula that will never let you down. It applies in advertising, although it doesn’t quite roll off the tongue as easily: ‘One: tell them what you’re going to sell them and why they need it; two: sell it to them; three: tell them what you just sold them and why they need to buy it again.