What to avoid at the negotiating table
Try not to minimise the other person's feelings (e.g., "What are you whining about? That's not so bad.").
Do not make negative judgments about what the other person has said, even if you believe what the person has said deserves a negative judgment (e.g., "These are just a bunch of lame excuses.").
Do not misrepresent or omit relevant facts. This can damage trust immeasurably if the other person catches - or even suspects - you are doing this.
Do not speak in a condescending or sarcastic way to the other person (e.g., "Well, so nice that you could take time away from your busy schedule to meet with me today!").
Do not demand that the other party apologise or admit to "wrong-doing." Most people won't apologize unless or until they believe what they did was wrong. Demands usually cause further resistance.
Do not make offensive or hostile non-verbal expressions (e.g., rolling the eyes, loud sighs, laughing, groaning when the other party speaks, or obscene gestures toward the other person).
Do not make threats to the other party. Even if you really intend to carry out a threat (e.g., filing a formal grievance or taking formal disciplinary action), making this threat against her/him in mediation is not likely to get her/his cooperation. It will likely set up a power struggle.
Do not shout at the other party. This may be very natural for you when you are angry, but it is not very likely to encourage her/him to cooperate with you.