Shooting For Realism
When working with ultra-low budgets, or when trying to add a sense of realism, you may decide against using professional actors. Most actors will require some kind of payment, you will have to work around their professional schedule, and you may even have to deal with the Screen Actors Guild’s union requirements. When working with non-actors you need to approach the situation in a particular way to help their performance along.
Make Them Similar
The import thing to look for in a non-actor is that they are similar in key ways to the character they will be portraying. Their natural mannerisms, demeanor, and appearance should be what you envisioned for the character ahead of time. They will not be able to go back to their craft to help construct the character so you have to make sure that they have it in them already.
Since performance and director interaction will be new to them it may be best to let them improvise more than you would a trained actor. If you let them add some of their own quick dialogue and allow for their blocking to be a little more spontaneous it will naturally distract from the fact that they are not a professional actor. Let them personalize some of the dialogue as long as it does not take away from the crucial parts.
You are going to need to look for people who are very outgoing and not overly self-conscious. This is great because they will be more willing to take chances and go the distance on screen. That is often the reason that comedians and musicians can take the natural leap into acting without formal training.
Do Not Use Them In Certain Situations
Avoid using non-actors who have an overwhelming disability if that is part of the script. If your film deals with things such as mental or physical handicaps it is better to use an actor because otherwise you run the risk of looking exploitive or that you are taking advantage of the people involved. It is really never advisable to use non-actor children because they have a very difficult time in a film production environment.
Use Their Clothes
Since you are using people that tend to be similar to the role they are playing it is best if they where their own clothes during the scenes. This will make them feel even more comfortable in the skin of the character and allow them to really perform. If you dress them in something they are not immediately used to they will have yet another standard to conform to.
Work With Them in Private
Make sure to rehearse with each of the non-actors personally ahead of time, communicating openly as to whom the character is and what you are looking for. Make sure that the expectations of them are well expressed before they enter into rehearsals with the other cast members. Let them try things out on you, and in this situation you have the freedom to direct them in a very personal way.
Know What They Are
The fact is that they are never going to look like professional actors on screen, so do not attempt to make them look as such. Tap into their spontaneity and lack of craft because that is where you are going to find your sense of realism.