Here is a small dollar store level on my riser, the bow is supported by odd old rags and left alone once the level is "level".

Then I take a bigger level and put it at a distance (actual distance is irrelevant).. This is where some guys align to the vertical line with a string, probably easier.

Then I look through the scope knowing the bow is level and turn the scope until my crosshairs are even with the distant level.

Then, more times than not, I use my 20 yard pin instead of the 30 yard pin and drive an arrow clean through my level..

When it is all done you can do this at 50 yards, every time. (this was all done from bench shooting of course)

I have every step on film, just holler if you need clarification on anything. It is a terribly easy process but in writing it can seem a bit tedious..