When you are working with non-professionals on the set, rehearsal is essential. Make sure your actors are very familiar with their blocking (the movement of the actor from one point to another), motivation for their lines and any “business” you may want them to perform while acting their parts. Business is a film term for the actions the actor may be doing to make the character authentic.
If you are shooting a scene with a mother, you may have her making sandwiches for her children before they run off to school. The making of the sandwiches is the actor’s business. A chef may be preparing food, a doctor performing surgery or a police officer cleaning a gun. It is essential that the business be well-rehearsed, so it looks very natural. Acting is more than delivering lines. It is inhabiting the character in such a way that it becomes real. Nothing is more distracting than watching a character perform an action he doesn’t understand or has not practiced and perfected. Non-professionals, if typecast, can perform quite well if they relate to their characters and are familiar with the type of business their character is assigned.