If you learn only one negotiating technique, learn to flinch. The rule is: Never accept the first offer. Any decent opponent will ask for more than they expect to receive, and you have to disabuse them of this notion. After all, the more eager you are, the more the other side will push; the more indifferent you seem, the more your opponent will concede.
You can flinch big or flinch small. Whether it's laughter or a subtle smirk, the important thing is that you react quickly and negatively to your opponent's first offer. Even if it's unbelievably generous, haggle--or at least grumble. And keep your glee to yourself. To professional deal-makers, the flinch must become second nature.
For example, there once was an attorney representing two entrepreneurs who made their hobby into a multimillion-dollar business. When it came time to harvest their company, they met their lawyer and fixed a selling price. An offer came--twice what they had hoped for! But their lawyer, in his excitement, accepted immediately. Had he flinched, he would have made a better deal. After all, his clients had a different number in mind!