You can find hundreds of books on the art of real estate negotiation... but, pardon my frankness, many of these books offer stale strategies and tactics that just do not work.
For example, in many books you can find the ABC rule - "always be closing." That is, you want to have a bunch of deals in the works and you want to get to "yes" as quickly as possible in order to close that deal.
However, getting to "yes" ASAP means you leave out a bunch of steps in the middle, such as carefully pre-qualifying your prospects by asking lots of questions. I call this process "Getting to 'no" first" - meaning, you weed out those who aren't serious about a deal.
It's also why I've simplified negotiation down to three cardinal rules: the person who mentions price first loses, get to know your opponent before you begin negotiations, and always get your agreement in writing.