You may not realize it, but you likely negotiate several times day. But what do you really know about negotiating? It's not something school boards have deemed worthy of being taught, so most of us go through life learning by observing. In Getting To Yes, Roger Fisher tells us how to be better negotiators.
It's not really about determining whether to use a hard sell (where you act like a jerk and don't budge from your position, thus putting the deal in jeopardy) or a soft sell (where you risk giving up more than you should have in an attempt at compromise/appeasement); instead, it's about finding ways to remove obstacles to making a deal that is the most efficient. This is the kind of deal where the to-be-divided pie ends up larger because of how the deal is structured.
I thought the book was excellent. It provides techniques both in dealing with counterparties as well as in thinking about how to advance not just one's own position, but also the position of the other side. I recommend it to anyone who negotiates frequently. (That's you!)