Start with high-confidence negotiating books, then narrow by subgenre or adjacent topics.
Kissinger the Negotiator
James K. Sebenius, R. Nicholas Burns
Perfect Phrases for Dealing With Difficult People: Hundreds of Ready-to-use Phrases for Handling Conflict, Confrontations and Challenging Personalities
Susan Benjamin, Benjamin Susan
Getting to Yes
Roger Fisher, William L. Ury
Get Anyone to Do Anything
David J. Lieberman
Top Dog
Andy Bounds, Richard Ruttle
Objections
Jeb Blount
Win Every Argument
Mehdi Hasan
Can We Talk?
Roberta Chinsky Matuson
Sales 101
Wendy Connick
The Challenger Sale
Matthew Dixon, Brent Adamson
Rapport
Laurence Alison, Emily Alison