Just recently I took a course call Real Estate Negotiation Expert put on the the Real Estate Business Institute. It was taught by Adorna Carroll (what a hoot!) - never a dull moment in her class! At any rate it was 2 days of great information, I'll summarize a little here:
It's important to know your own authority, ability and strengths; do NOT underestimate these.
Never ASSUME you know what the other side wants.
Do not OVERESTIMATE the other side knows your weaknesses.
NEVER become intimidated by the side's rank, accomplishments, or prestige.
Do not be overly influenced by taditions, statistics, forecasts .... the old "we've always done it this way."
(These were the errors according to the Harvard Law School on Negotiation)
The whole purpose is of course to get to the best possible outcome for your client. Just make sure you unterstand their motivation, urgency and the details of the other side as well as your own. You want to make this deal a WIN-WIN for all - and it IS possible.
One of the reasons for deadlock is when one of the parties states "Take it or leave it". This is never going to end well. Another reason for deadlock is letting egos get in the way - leave yours out! And also be careful of tempers - they have no place in an artful negotiation.
Recently I also read an article on negotiating in The Bottom Line. It also had some great ideas. Most of us know about "mirroring" - doing the same thing the other party is doing: sitting back when they do, etc. This article went further by stating repeating the last 3 words the other party says makes them feel you really understand what they are saying. Also it stated to expose the negative thoughts quickly. The other party may be harboring these fears so it's best to get them out in the open. Another idea was when dealing with numbers (we tend to do that ALOT!) to come back with a number that appears to have been carefully calculated: Rather than $2,000, come back with $1,883. It sounds like there has been careful consideration before answering.