The better your understanding, the more flexibility and creativity you'll have as you create options. Talking gives this advantage to the other side. Know the authority of each person in the room. Make sure you know whether or not you are negotiating with someone empowered to make the final decision. If you aren't, make sure you present options in such a way that they meet the perceived needs of the negotiator and the other members of their organization.
Large concessions indicate that a lot more can still be conceded before the bottom line is reached.
Rapid or large concessions undermine the credibility of the initial offer. All concessions teach the lesson that more concessions will be made. Never make concessions expecting that the other side will meet your terms on the next issue. On the contrary, they will expect more concessions. Never be bludgeoned into splitting the difference.