I've read a decent amount of self-help over the years and I've read Dale Carnegie's 'How to win friends and influence people' and the core message of the book was to be a nice person and people will want to be around you. I'll be honest I may be remembering it poorly since none of the book particularly stuck a chord with me. There was even a morally questionable chapter about being nice in such a way that almost seemed insincere and nearly sociopathic, that was just one chapter though.
The two self help books I've found to really help were a book on emotional intelligence and a CBT book. (Emotional intelligence by Daniel Goleman (I think & Feeling good by David Beirne) Both books helped me improve my mindset or perspective and unlike a few of them, weren't trying to sell me something.