Separate the people from the problem
It’s not enough to address the problem objectively. Every negotiation also involves people. With people come people problems that are separate from the main issue at hand.
First off you need to understand the other parties perspective. They might not see things the same way. They might hold biases. Or they might feel like they didn’t get to participate in the process and are getting a solution force onto them.
You need to consider their emotions. Let them vent if they need to. Express your feelings. Let them know how you feel not what they did or how they made you feel. And don’t react to their emotional outbursts.
Most importantly, focus on the process of communication. This means listen to them and treat them as an equal in the discussion.
By putting addressing these people problems up front, you build a stronger relationship. A stronger relationship makes for better future negotiations. By tackling the problem together you become partners instead of opponents.
Book: Getting to Yes