If you know a meeting is going to be contentious ground rules can be especially helpful. Ground rules are guidelines that meeting participants are expected to keep in mind; expected to follow during the meeting.
When the facilitator explains ground rules at the start of a meeting that provides a perfect opportunity for the facilitator to explain his or her philosophy, style, and general expectations for the meeting.
In this video Craig models how to explain ground rules for a meeting that is expected to have some conflict. Craig made this video live on location just before the start of a meeting.