The parties should try to put themselves in the other's place. The parties should not simply assume that their worst fears will become the actions of the other party. Nor should one side blame the other for the problem. Each side should try to make proposals which would be appealing to the other side. The more that the parties are involved in the process, the more likely they are to be involved in and to support the outcome.
Emotions are a second source of people problems.
Negotiation can be a frustrating process. People often react with fear or anger when they feel that their interests are threatened. The first step in dealing with emotions is to acknowledge them, and to try to understand their source. The parties must acknowledge the fact that certain emotions are present, even when they don't see those feelings as reasonable. Dismissing another's feelings as unreasonable is likely to provoke an even more intense emotional response.