https://www.amazon.com/Nonviolent-Communication-Language-Lif...

It is one of those compact books that are quite effective. Other books are a bit heavy and you almost feel like you have to memorize flow charts. This book is fairly formulaic, but with easy to remember formulas. A lot of the book may seem a little too soft/touchy, but fortunately when I read it I was reading other books that go into the details of the psychology behind communications (which this one doesn't), and there is a lot to back up the advice in the book.

Mind you, if this isn't your default style of communication, it will take a lot of practice (and perhaps years) to get there. I think for me it was about a year of trying before my first successful use of it in a hostile conversation. It's hard to stick to trying something if you don't see signs of success inside of a year.