ORIGINAL: GregH
Once I get in my stand and get my bow ready, I draw it back and check the peep and pins. When a buck shows up, I study it to see if I want to shoot it. If I don't want the buck, I calmly watch it go by. I remain still and hidden and don't make any unnecessary movement until after he's gone. I don't practice draw on deer. I used to, but not anymore, I don't want to take a chance of spooking it.
If the buck is one that I want to shoot, I immediately concentrate on where he's going and how I'll be able to stick an arrow where I want it. My focus is so narrow that I can't even see the horns. Don't look at the horns, keep your eyes on the target, the exact spot you want to hit. That way the horns won't distract you and you'll beable to get off a better, more relaxed shot. I have killed 2 bucks that have gouges in their racks from broadheads. Someone was looking at the horns instead of concentrating on a spot.
So much happens in such a short amount of time, it is unreal. It seems that time is in slow motion. While the deer is approaching I scan back and forth from the spot (target) to the lane where the opening for the shot will take place. During this time my bow is pointed at the bucks chest with my arm fully extended. I've had to hide behind my bow at times. I'm trying to find a place, before the buck gets in my lane, where I can draw my bow undetected. A lot of times this is when the bucks head goes behind a tree. These spots are planned out ahead of time before the buck shows up. That way I'll automatically know what to do when he does show up.
Pick a spot and focus on it. Do not look at the horns anymore. You'll get plenty of chance for that when he's on the ground. Don't count your chickens before they hatch.
BTW, now days I get the shakes after the shot, not before. I credit this to the extreme focus on my spot. I think that this is a good approach to getting a calm well placed shot on your buck.
Good luck
There should be a book in the bible named "GregH buck hunting"