Think of diamonds and pearls, two of the most precious and expensive baubles on earth.  Diamonds are plain old carbon put under tremendous amount of heat and pressure.  Pearls are the result of a tiny piece of sand or grit.  Most directors work this way.  Either pressure the performers or keep nagging at them when the director's results are not immediately realized.  I prefer a third method which I think of as sculpting.  Warm the clay in your hand until it reaches a workable level of malleability, gently shape and mold, and before you know it, you have created an atmosphere of complete trust and support that will enable your actors to attempt anything you lay before them .  This has never failed to work for me.