It all depends on your projectile and its tragectory. If your hunting with a rifle with a scope and in a stand its best to aim a little low if the animal is up close say less then 100 yards. 2 inches lower than a straight on shot would be. The greater the distance the less compensation is needed.
Same goes for an arrow aim slightly low in a stand whitetail tend to duck arrows anyways if this happens you will still hit both lungs.
If im hunting with a shotgun with buckshot i will just throw my bead on him and pull the trigger 00 buckshot usually does the job regardless of an inch or two shot placement.
Hope this helps its just how i shoot may not work for everyone just how i was taught.
This information gives you the distance correction for firing your rifle at an angle. Lets say you are in your stand and your target (Buck of a lifetime) walks out 250 yards in front of you and presents you with the perfect broadside shot. Your rifle is zeroed for 100 yards and you have figured the angle at 40 degrees. You will multiply 250 times the COS for 40 degrees to get your corrected distance of 187.5 yards. Then just dial your scope for 190 yards and hold dead on. Hopefully you have done most of this work before your target ever presents itself by doing a field sketch and ranging various objects and figuring the angles for the different ranges.
The other thing to do is to imagine the target in 3D. If you try the heart shot at a bit of an angle, you could shoot under the heart because the bullet is traveling on a downward plane. You have to aim past the ribs and where the heart is, not where it appeared on that paper target you shot at all summer. This is more of an issue for bow hunters, but can also affect gun hunters. It really depends on the angle of the shot.
With my 30-06 sighted in at dead on to a level target at 100yards I would sight in dead on an animal at 100 yards from a stand. 50 yards I would sight a couple inches lower since it shoots slightly higher ast 50 yards. Depends on your ammo brand, caliber and what range you have it sighted in for.
With a rifle, I'd not worry about any shot from a treestand, except for two things. 1. If the animal is very close and your shot will be a raking, high angled shot from above. Then, as already stated, you'll simply have to visualize the bullets downward path through the body, and aim accordingly.
2. If at extreme range (beyond MPBR) and an added angle is involved, either uphill or downhill, then you'd need to aim lower, compensating for the shorter distance gravity effects your bullet/shot. On long angled shots, up or down, the actual distance is governed by the actual horizontal distance, not overall distance to the target.
Uphill or downhill shots do not become critical until you are shooting beyond your MPBR for that caliber/rifle (set by you when sighting it in).
Hunting is not usually a pursuit where instant gratification abounds. It takes a lot of time, practice, resources and patience to be a successful hunter. So when someone decides that an area they hunted only once without taking an animal is worthless and devoid of game, I don't quite understand it. These people usually jump from game management unit to game management unit; trying a new one every year.
Now don't get me wrong, there are people that just enjoy scouting and hunting...