Be positive. Movie production is a long and tedious process and the better the cast and crew’s attitude, the smoother the shoot will go. Be pleasant to work with and don’t have an attitude. No one likes egos, especially egos from actors. The crew arrives much earlier and leaves much later than you do. They work hard and become very frustrated with egocentric actors. Remember that everyone in the production process is equally important.
Directing actors is the primary function of the director. Work closely to help them understand where their characters are at any given point in the story so that they can deliver a believable and realistic performance.
All too often, directors are technically adept and understand where to place the camera and how to work with the crew but they do not know how to speak with or work with actors. Few directors have ever acted and, thus, lack the understanding of the actor’s process.
excerpts from "The Power Filmmaking Kit", by Jason J. Tomaric