Develop a clear vision of what you want portrayed before you work with the actor. Define the objects and actions to be portrayed for yourself so that you can clearly communicate them to the actor. Make certain that you understand what the piece is trying to relate so that you can help your actor.
Discuss the piece with the actor to achieve a mutual agreement on the piece's purpose. Determine the actor's concerns about the piece so that those can be resolved during the rehearsal process.
In rehearsal, focus first on the overall flow of the action. Try to help the actor find the mood of the piece before working on small details. An actor's confidence in a piece is critical to its success. Understanding the overall flow will help build that confidence.
Work on details one at a time. Make sure the actor can accurately portray each step of the piece before moving on to the next. You don't want the actor to concentrate on the stuff he or she finds easy and skip through the difficult parts.
Find the physical items the actor must pantomime if they are unfamiliar. Many actors, for example, have never actually handled a gun. Provide a toy gun for the actor to work with until he or she can memorize its shape and functions.
Work with the actor on common actions to make sure they remain realistic. Actors can sometimes over-exaggerate simple actions like peeling a banana -- peeling the whole fruit when, in reality, one only peels back enough to get a bite, not the whole thing. Pantomimed driving, too, needs to be watched for accuracy. There's a tendency to work the steering wheel back and forth to show the "action" of driving. But driving is a smooth, subtle activity occasionally punctuated by simple turns. The actor's eyes need to stay on the road ahead in order to maintain the illusion that the car is moving.
Keep the pace of the piece in mind. The actor will naturally go slowly until the various actions are memorized. Like good dialog, a pantomime piece will be powerful if it is carefully timed.