You can do this mentally with yourself, but it generally works better if you can enlist the help of another person to play the role of the other side—the person or group you will be negotiating with (i.e. play the role of the Devil). Have your Devil’s Advocate plead the other side’s case; take their anticipated position; use their arguments and objections. You should try to estimate your Devil’s desired outcomes and goals (BATNA). Do this prior to your negotiation. It provides you an “inoculation” in advance of the negotiation and helps assure you appropriate responses and strategies in place. Remember, the other side may be more intent on frustrating your proposal than accommodating it.