Manage the "people" side of the meeting, so that the Leader can manage the "content" side, by making sure everyone contributes to the discussion, preventing speakers from interrupting others, and protecting people from verbal attacks.
Monitor time spent on each agenda item, and keep Leader and Participants within the time frame allotted to that item.
Listen for discussion " drift " and get everyone back to the issues at hand. Emphasize the meeting objective, if necessary.
Monitor people creating problems and deal with themtactfully, but directly.
Refrain from offering your own opinions. Mediate conflicting opinions .
Suggest other approaches when a process isn't working.