There's nothing I like to study more than techniques of persuasion, and I want to persuade you to check out a website called ChangingMinds.org. You can think of it as Robert Cialdini, my hero when it comes to persuasion, on steroids. Here is a direct link to theories of persuasion but do spend time on other theories such as power, friendships, and emotion.

Haven't taken this course, but I bet it's useful: Managing Without Authority Alok Jain: Thanks for the tip!.