If you haven't already read How to Win Friends and Influence People, you definitely should.
One of my bosses made a difficult coworker take a Dale Carnegie class. Afterward he said that it "changed his life." I thought it made him even creepier with the constant fake smile, eye contact and repetition of people's first name in conversation.
For example, he points out that most people never accept blame for anything. From CEOs to convicts, we generally blame our failures on circumstances or other people. So with this in mind, he gives ways of steering people away from errors without raising their self-defense mechanisms or forcing them to admit that they're wrong. After all, do you want to defeat and humiliate them, or do you want to help them?
Indeed, the reason I liked the book was that generally, it DIDN'T seem fake. It encourages you to genuinely care about people. And says that, as it happens, this actually works better, too.