Negotiating is a two-way street. Before you start the process, determine what you expect in return from others if you give them what they want. Simply be so good at what you do and what you offer that there isn't any room for negotiation. The more credibility you have, the less you have to negotiate. If any one relationship takes an inordinate amount of your time, is hindering your effort on more promising opportunities, and is high on the "pain" meter, it might make sense to walk away.