First off, Here's what I do.

When I see a shooter buck, I immediately dont look at anything but the kill zone the entire time I decide to take the deer.

When I get drawn back, and the situation allows, I hold the pin on him for 5 seconds before I even begin to pull through the shot.

I use back tension and let the shot be a surprise and concentrate only on the spot I want to hit, and my follow through.

And most importantly, dont think about how great his rack will look, or any other aspect. This will only deter your concentration from the shot. Which if you practice, is one you've made countless times before.