@Robert Gentel,
Let me elaborate very briefly:
Some fundamentals to negotiating is to focus the discussions on what you want to achieve and what your interlocutor's goals are as well. You can never loose sight of what you are trying to get, even as things get emotionally heated (e.g. you might want to call the guy an asshole but if you want something from him keeping that goal in mind might indicate to you that it is not always the greatest idea in negotiation). Find common ground and work toward reaching mutually satisfying agreements (the notion that a good negotiator is a hard-ass is a false stereotype, when that approach works it only does out of a position of power and not negotiation and it actually hurts negotiations. One key principle to remember in negotiations is that you usually have to negotiate with the parties again and raking them over the coals is something you can get away with if you already had the power to do so, thusly not really needing to negotiate anything, but will reduce your ability to find good partners in negotiation in the future).
You should also know your best alternative to a negotiated settlement at all times and not overplay your hands. For example, if you were to demand that Mexico build a wall or that China bend over and take it in the rear you should note that you do not actually have any power to compel them to do so if they tell you to pound sand. You would then realize that making such demands is foolish theater, not sound negotiation.
