Pick your spot, a clump of hair, a shadow of muscle curve, whatever is in your kill zone.
Once you commit in your mind to taking an animal you need to stop thinking about it. Your done. In your mind tell yourself this is the animal and from that point do not look again at anything except finding your spot.
take a couple of deep breaths thru your nose and out your mouth slowly.
Focus only on your spot.
There are no vines, no twigs, only your spot.
When you practice practice the same way. Three D shoots are great, but if you are mainly a tree stand hunter that should be your main practice.
Learn to utilize a second anchor point, often when guys are hunting and the heart is pumping away they do not come to full draw or they draw and pluck off the string.
To do a second anchor point pinch your pinky and thumb together when you shoot. Draw, think only pulling back your elbow, not your hand.
When you get to that spot that you put your finger for a anchor point, pull your elbow back further and lay your pinched down thumb along your jawbone and press it in there ( second draw point).
You will find that this will prevent you from short drawing which is the major thing that bowhunters do under stress.
They try to freeze time at the point where it looked like it was right, they release in different points and end up torqueing the bow string by plucking it.
The second anchor point as done by Hill and demonstrated by the great John Shultz is the single biggest improvement for the bowhunter especially.
Try it, pinch down your pinky with your thumb, touch your corner of the mouth or whatever you use with your finger and lay your thumb right along your jaw.
Once you get that feeling and practice with it you will no longer short draw or pluck your bow off line under stress.
Also when you go out to your treestand bring a few judo points or field points and take a shot or two while your in the stand. Focus, draw back your elbow, not your hand, pick your spot, not some obvious bright leaf but a shadow behind a stump, pull your elbow back until you hit the first anchor, then the second, pull your hand back to release as you push towards your spot and you will have meat on the ground.