Los of good advice above , but above all keep a hair picked out and never take your eye off it and cant your bow when the deer are close.
Now you have the optical part to deal with , try this little experment .
1) Take a 3d target and put it 10 yards from a tree stand 15-20 feet up a tree .
2) Put a orange sticker the size of a quarter half way up the deer in the middle of the kill zone.
4) climb the tree with safety belt on
5) HA you can't even see the orange dot can you
6) now do you see why you shoot high ?
7) You think you are shooting at the heart but are actually shooting at half way up the deer !
CURE IT ALL BY PICKING WHERE YOU WANT THE ARROW TO EXIT!
I read about this 25 years ago by Smiling Chuck Adams - yes it was good advice .