The single most important thing a director can do in order to get better at directing actors is...to take some acting classes. Directors have to understand the acting process. They have to understand it from the inside.
There are things a director can do to help them prepare for the direction of actors in a scene that should NEVER BE COMMUNICATED TO AN ACTOR. For example, the advice in this article to write a word on the storyboard describing the main emotion of a scene, or to create an emotional journey map of a scene. Make adjustments on set with a verb not an adjective - tell an actor to do something, not to be something. For example say "Punish him" instead of "be more cruel".If you say these adjectives and emotions to an actor, then these things are the kiss of death to directing them. Not only do they betray a complete misunderstanding of the acting process but, on set, they will require your actor to exit their subjective headspace, adopt an objective perspective and deliver a bad attempt at giving you the result-oriented direction you have asked for. Unless you have a very experienced and skilled actor, who can reinterpret your approach, you will have sucked all spontaneity and therefore believability from the performance. Surely every director knows that one of the most insulting (not to mention ignorant) things you could say to an actor would be something like 'the attitude you played in that scene was...'.
Wu understands that in screen acting the actor's process requires maximum subjectivity and vulnerability. Giving direction adjustments in private (which may only mean quiet tones on set) respects the creative space. It does not drag the actor into objectivity and it does not ask the actor to put on a 'public' face in between takes. This is the mark of a good director who understands the acting process. I know I'm working with someone I can trust when a director talks to me like this.