Dale Carnegie's book "How to Win Friends and Influence People" provides techniques for improving relationships and becoming a better leader. It was first published in 1937 and has since sold over 15 million copies. The book outlines principles for dealing with people such as avoiding criticism, giving sincere appreciation, being genuinely interested in others, being a good listener, and talking about other people's interests. It also provides guidance on how to change people's minds without causing offense and how to be an effective leader through praise and building trust. The book continues to be widely relevant for improving interpersonal skills.