If at all possible, get up in a stand and try it before you go!
I cant tell you if you need to aim high or low or dead on - I practice from both the ground and a stand, so its all kind of "instinctive" for me. But I can tell you that shooting straight down, I missed badly the first time I tried it. Took a half dozen arrows to get that dialed in.
When I get out early, I bring 1 or 2 field points and stump-shoot them as soon as I get strapped in.
And as stoker implies, remember that you are aiming for the heart inside the deer, so the spot you pick to hit needs to be higher on the body.
good luck, sounds like a fun hunt