I once skimmed "How to win friends and influence people". I didn't read enough to have a good opinion of the advice (I suspect djcb's description of it being fairly good advice as long as the author's experience generalises well, which HTWFAIP probably does better than many but not perfectly).

However, what had a profound influence on me was that though there's an unfortunate stereotype of people who've read too much Carnegie seeming slimy and fake, the author seemed to genuinely want to like people and be nice to them, which I thought was lovely.