Like everyone else, I thought I was good at negotiating, then I read this book. This is not how to "beat" the other guy, rather how to forge long lasting relationships where your counterpart says "yeah, I'd deal with you again". The best take-away for me was the accusation audit, and learning that "no" is only the beginning.
I tried reading a few books on negotiating in the past. Chris Voss' book is written in a way where his principles and rules are easily understood, combined with example situations and dialogues. It's not too technical, not too focused on business, but on real situations you can see yourself using the techniques on.