Use the KISS system.

Here's the best way to do it...Locate some trees or other objects near where you think the deer might be coming by your stand location. Now range those trees STRAIGHT OUT from your stand (at the same height you are). THAT is the distance you will need to shoot if a deer walks near one of those trees. You have to shoot the linear distance (or the distance from the base of your tree to the deer).
Don't be deceived....Let's say you are 25 feet up in your stand and you use your range finder to range a deer. The reading comes back as 16 yards (or 48 feet). If you set your pin to shoot at 16 yards you may shoot over that deer because you want to shoot the linear distance to that deer which would be 13.65 yards (or 40.97 feet).

I agree with the rangefinder. however if u cannot afford a range finder, then one will not be appointed to you, lol!! No seriously, perfect practice, makes perfect.

I like the KISS system too!

Hunt a steep hillside it will really keep u on your toes. I dont want to create confusion but a range finder really will keep the error margine to a minimum.

This is an interesting topic. The truth of the matter is the only distance you are concerned with is the portion of your arrow's fligth path affected by gravity. In other words, you do not care about the slant range to your target, you care about the ground covered by your arrow. As stated above, pace off the distance on the ground radiating out from your tree stand. Do not worry about the slant range from your elevated point to the target, worry about the distance from the tree to the target, not the tree stand to the target.

When trying to convice people of this argument, I use the following scenerio. If you were in a really high tree stand, say 30 yards (nose bleeder, and yes this is probably too high so use your imagination), and you have a 20 yard pin and a 30 yard pin and a deer walks right under your stand. What sight pin do you use, the 20 or 30? Since your are shooting straight down, you would use the 20 yard pin. You are really shooting point blank at the deer. Now granted any mistakes you make like torquing the bow or punching your release will cause your arrow to move off of your intended target more than an actual point blank shot. If the deer was 20 yards from the bottom of the tree, then use the 20 yard pin even though the slant range is different (slant range = distance from you to the deer, the 'C' part of the triangle).

This also allows you to use the KISS (keep it simple stupid) method mentioned above, and it is correct.

OH Redneck