First of all, instead of thinking of a negotiation as a process where you divide up a fixed pie of whatever it is you are negotiating over between the parties, meaning every little bit you gain will necessarily be a loss on their side (and vice versa, a so called “distribution game”), you want to become creative and extend the pie instead. This pie-expansion mindset is inspired by William Ury, co-founder of Harvard’s Program on Negotiation and together with Roger Fisher father of the so-called “Harvard Method”, built around inventing options for mutual gain.
To uncover underlying interests, questions are your friend. Ask a lot of them, in a problem solving manner (“Why, What if, What is your advise, What makes this fair, …), and be certain to always formulate them openly. This way, you and the other party can engage in joint problem solving, and become partners in uncovering a deal that brings you way beyond your respective BATNA.
Moreover, keep in mind that there is much more to a negotiation than the factual level. There is always a wide variety of interests of the other party you can meet without even giving in on the facts - but rather with taking extra care of their personality, of their needs and fears beyond the factual outcomes of the negotiation. If you managed to execute joint problem solving and expanded the pie in a satisfactory manner for both you and them as a first step as suggested above, it is quite likely that you are at a point in the negotiation process at which facts aren’t even that important anymore. You can ensure mutual satisfaction by going beyond the factual level and consider things such as their pride. And if that doesn’t seem to work just yet: go back and dig deeper into the sea of interests and come back to this later.
With these two strategies, which may be summed up to “be hard on the facts, but soft on the people,” you are sure to use the time you bought at the negotiation table by giving the other party a reason to stay to reach an agreement that is better than your BATNA - and with a little bit of practice and feedback it will certainly be much better than your and also their alternatives.
One more closing remark on Jim Camp, the author of the definition that sparked these thoughts on negotiation: complementary to William Ury, who we learned to be a strong advocate of “Win-Win” approaches, creating mutual value gain, Jim Camp’s signature phrase and the title of a book rebutting Ury’s ideas is “Start with No.”. It is remarkable that, although Camp is a supporter of hardball negotiating, Camp’s definition made us end up with a lot of Ury’s ideas. For me, this is a strong indicator that neither theory is viable on its own, given the variety of negotiations you will find yourself engaged with in your personal and professional life. Rather, to be a skilled and versatile negotiator, you need to be familiar with both schools of negotiation, and learn to decide which aspects of either one to use in any given situation.