If you listen well, your response is far more likely to be something to which they will react favorably. Keep a clear head. This may require taking a time-out to rethink your approach. Perhaps the last point to make about the negotiation process is that you need to know when to quit. Know how to indicate agreement has been reached.
Negotiation is a process civilized people use to reach agreement.
The goal of negotiation is not to win, it is to succeed. The mechanism of successful negotiation is collaboration, the work of a partnership rather than a means for kicking butt. During the negotiation process, pay attention. Listen to others. Treat them with respect.