It can be very difficult getting people to let go of their inhibitions.
They see others sitting out there in the audience, even in rehearsals,
and don’t want to look foolish. But that is the essence of acting;
looking foolish.
So as a director of amateur actors, you need to draw that tendency out.
Not all of your actors were the class clown. So one thing that can work
is to get your actors to do silly things in rehearsals to desensitize
them to doing them for the main event. That’s the theory anyway. It may
work for some people. Under stress, anybody can react in any different
way possible.