You will know when you are high enough or too high for you can't pull you BVD's out of the crack anymore!!!!!
Seriously though, I agree with what the others have said here 100%. Your area and sorroundings will dictate on just how high you need to go. I just hung my highest stand last year and it is 30 feet to the base of the seat. I also jacked up my left tri-lat muscle doing it as well putting in the nearly 30 screw in steps. And thats with a step assist, we call it, to help screw them in. I am just first able to be able to use that arm like it is supposed to without shooting pain upto my left ear or clear to my spine in the left side. JUST began to be able to draw and shoot my bow without fear of dropping/releasing it during draw. I have 4 ladder stands to be put up for I don't want to re-injure so soon. They are 16ft. We will see.