ON ACTING: Don't Put the Cart Before Horse
Good camera technique inevitably follows from good acting technique; and a smart actor never puts the camera cart before the performance horse: making the serving of the meal more important than the good cooking.
The good actor first make sure their acting performance is worth the audience seeing and hearing.
I have found invariably and actor's poor camera technique generally results from the actor's lack of confidence in their acting abilities. So when they act in front of the camera's, they freeze up.
When an actor has confidence in the acting abilities, on the other hand, has honed his or her good acting technique to the point that they know they will always be good, it doesn't matter when or how someone is watching them; and whether that 'watching' is in close-up. or two-shot or master shot, or from right profile or left profile.
First learn to cook the good acting meal; learning to serve it will be a breeze.