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First, like an actor you have to control yourself. Completely. If you cuss a lot, you need to cut it out. If you are short-tempered, grow patient. If you easily lose your train of thought or need frequent breaks, learn to follow through. If you are disorganized, get organized. If you are easily distracted, learn to focus. And so on and so on. Obviously you can take this too far and make yourself a bundle of nerves, but realize some behaviors just won't cut it for a classroom teacher. I can't list them all, but watch how your students respond to you and search your heart. Does your temperament suit the kind of class you are trying to create? Can you change it?
You can't change everything at once, but you most certainly cannot do the opposite either, and the opposite is another cliche, be yourself. In fact, that's probably the worst thing you can do.
Second, teaching is performative because ideally the teacher should disappear and the impression left upon the minds of the students should be that of the material. This doesn't mean that your zeal, style, and unique take on the material are irrelevant, but that they should serve the understanding of the content and not take center stage.
Here too are the extremes instructive. Some teachers are too much of a presence in the class. Too much talking, interference, jokes, asides, theatricality, and so on. Although they are usually enthusiastic about the material, they overwhelm it. Other teachers are nonentities in the room. Usually by lack of discipline or just by being boring, they don't bring the material out of the realm of concepts into the real world. The lesson is dead on arrival. Now you don't need to be a cheerleader, but kids need to see some heart.
In a nutshell, students need to see someone animated by the knowledge that they are articulating. They need to see only those parts of you, and those parts controlled, that let the ideas shine out. Like an actor on the ancient Greek stage, some of you will disappear behind the mask and some of you will be the medium for the ideas. Unlike the actor, though, you have no physical mask and you need to possess the understanding of yourself to decide which parts of you may and should come forth for the sake of learning.
It is a tall order and its prerequisites are not vanity and narcissism but discipline and self-knowledge, but through such teaching "performance" students will see ideas neither dull and etherized for dissection on the table, nor just barely peeking out from under your personality, but alive, present, and deserving attention and concern. In this way the teacher transforms the knowledge, the student, and himself.