We use the "principled negotiation" method adopted by the Program on Negotiation at Harvard Law School (where we have studied and taught negotiation and mediation). This approach to negotiation is explained in "Getting to Yes – How to Negotiate Agreement Without Giving In" by Fisher & Ury and similar leading books such as "Getting Past No" and "Beyond Machavelli".
This method involves a systematic examination, from the standpoint of all stakeholders, of
the available alternatives to agreement in order to identify everyone’s BATNA (best alternative to a negotiated agreement)
the interests of each party
objective criteria of fairness
creative options
durable commitments
in a process which involves effective communication and building good working relationships.