Ha! I came here to mention "How To Win Friends and Influence People" as well.
I read it more when I was around 38 or so, but it really helped me change how I interacted with people.
While it's ostensibly a book about sales, I took it as breaking down selling into the idea that if you get along with people and they like you, they will want to work with you. That can take the form of making more sales, but I took it as having people want to do more with you and be around you more.
And how does that happen? Kinda simple: be nice to people, be genuinely interested in them (even if their interests aren't your core ones, they still are often curious), and genuinely try to get to know people.
I took this as a great life lesson for making friends and getting along better with the whole world. And from that flows nice things. And if it's what you need/want, more sales. But it doesn't have to be about sales.