Time, mostly. Nervous patients get the first slot of the day when the practice is quiet, and a longer one so nothing is rushed. Rushing is what makes dental anxiety worse, and a practice with a twenty-minute slot cannot avoid it however kind the dentist is.
A stop signal agreed before we start — raise your left hand and everything stops immediately, including mid-drill. It sounds trivial. It is the single thing patients tell us made the difference, because most dental fear is really fear of not being able to stop.
And no surprises: you are told what is about to happen before it happens, in order, including the parts that will feel odd. If you would rather not know, say that instead and we will stay quiet. Both are fine; what is not fine is guessing which you want.