More data points:
I just finished reading Crucial Conversations: Tools for Talking When Stakes Are High by by Kerry Patterson, Joseph Grenny, Ron McMillan, and Al Switzler. This is a quick review of the book.
I can summarize the whole book for you in roughly the space of a tweet:
Difficult conversations require safety. Establish safety by listening, empathizing, and suppressing emotional reactions that would make others feel unsafe. Once you have created safety, be honest and straightforward. Work together towards mutual benefit. Respect each person's interests.
If you don't know how to do those things, reading this book might help you, as the authors provide some techniques. The techniques they offer are shallow, though, so they're only likely to be helpful if you've never made a serious attempt at communicating or negotiating effectively. If you've tried at all I think you'll be left wondering when the book will go deeper. Warning: it never will.
Personally, reading this book was a waste of my time. I'd already gotten all the big ideas in it from other books. I think I feel pretty confident in saying that you only need to read approximately two books about having conversations and negotiating to learn all the basics (you'll need a lot of experience to get good at putting the ideas into practice, though). Here's some other books in this space you might consider for your ~two (there are many more):
For myself, I think the one I found most useful among all of these was How to Talk So Kids Will Listen. My second pick is Games People Play.
If you just want the theory that powers the ideas in all these books, I think you can learn it from studying two things: game theory and transactional analysis. Game theory you probably know or are at least aware of. Transactional analysis is a fake framework in psychology; it's wrong in some important ways but extremely useful for getting a baseline understanding of why people do the things they do in social interactions. It's not the whole story but it gets you more than halfway to learning to notice pathological patterns of communication.
My final take on Crucial Conversations: it's a breezy book that will at best make it clear that it's possible to communicate effectively and to change the world by talking. Most of the techniques and frameworks offered by the book are too shallow to be really useful without experience or prior knowledge to flesh them out. I think the book's success relies heavily on readers who are primed by experience to be able to fill in the blanks. I recommend against this book and think you should read How to Talk So Kids Will Listen instead.