Better to bend at the waist as these guys are saying, but if you can't you have to practice aiming low. Deer will often come right under a stand and you have to practice those shots or you will miss by shooting too high. With no practice, its tough to pick a small spot to hit and then aim lower. In the back yard, try putting one of those bright orange stickers the size of a quarter right in the middle of that ten inch circle you are hitting. Shooting at such a small spot will help condition you to shoot at an extremely small spot on the animal and your groups will get very tight. For your last few shots at the target always take the sticker off and try to hit the imaginary dot just like if you were shooting a real deer.
If you see a deer you want to take, as soon as you decide it will be yours, STOP looking at the deer and pick a small spot you want to hit on the body. Even if it's 75 yards away. Then as it gets closer just zone it on that one spot the whole time until it gets into your range, then shoot the imaginary orange dot ! I have not missed an animal since I started doing this, but I probably just jinxed myself by saying that.
I practice from my roof.