Experience. Sometimes when I see deer I am not going to shoot, I go through the motions anyway. I draw, settle and anchor, then let down.
Mobo....I got crucified in here by a certain forum member for this practice.....but I did it my first year a few times (and I never put the actual pin on the animal). I think this is good "practice".
I've found that the more deer I'm around.....the more calm I am....BUT....I GET VERY WOUND UP when a big deer is in my presence. I hope I always do. I wish I could bottle that feeling and sell it. If I ever lose it.....I'll quit hunting.