12 Ways of Winning People to Your Way of Thinking

Rule 1: The only way to get the best of an argument is to avoid it.
Rule 2: Show respect for the other person's opinions. Never say, "You're wrong."
Rule 3: If you are wrong, admit it quickly and emphatically.
Rule 4: Begin in a friendly way.
Rule 5: Get the other person saying "yes, yes"" immediately.
Rule 6: Let the other person do a great deal of the talking.
Rule 7: Let the other person feel that the idea is his or hers.
Rule 8: Try honestly to see things from the other person's point of view.
Rule 9: Be sympathetic with the other person's ideas and desires.
Rule 10: Appeal to the nobler motives.
Rule 11: Dramatize your ideas.
Rule 12: Throw down a challenge.

Source: How to Win Friends and Influence People