Separate the brainstorming from the decision-making process. Look for areas of agreement by identifying shared interests. Look for ways to dovetail differing interests by exploring options that are of low cost to you and high benefit to the other party and vice versa. These criteria may range from current market value to procedures for resolving conflict, and will bear directly on your ability to come to an equitable final agreement. Standards such as these are also crucial to establishing a foundation of trust on which to build a relationship.
Principled negotiation works well because it is outwardly focused.
Standard positional bargaining, on the other hand, focuses entirely on self. The first establishes common bonds and a shared search for solutions. The latter produces isolation and engenders ultimatums. Either may result in agreement, but the first builds relationships for the future while the second often leads to resentment and distrust. Principled negotiation is especially crucial when an imbalance of power exists between the parties.