Mutual understanding is a necessary precondition to reaching an agreement. Preparation is the best path to mutual understanding.
Preparation includes much more than analysis of each party's interests.
Preparation includes analysis, perception, prioritization, anticipation, and development of objective criteria as well as options for mutual gain. Your analysis should identify the relevant legal and business issues. The emotional component of my perception must not be overlooked. Know yours and know theirs. You will most certainly miss a golden opportunity or you will react caustically to statement born of frustration unless you anticipate both your reactions and your opponent's reactions to the topics and the sequencing of topics.