I always make sure the rifle fits first before positioning the scope. That means having the length of pull adjusted either with adding spacers or cutting back the stock. It's also a good time to add a butt pad you are happy with. The shooter should be able to shoulder the rifle without stretching your neck forward or leaning you head over to see through the scope. Sometimes I will just take the front scope ring off altogether and use a slightly loosened rear ring to help me find the right position and then I will look for scope rings or bases that allow me to keep that position. Another trick I use sometimes with other shooter is to take the butt pad off their rifle and see if it shoulders better for them. It often does and that gives an indication the stock should be shortened. The height of the rings is important as well and it has become traditional to use the lowest rings you can get away with regardless of the drop, (or rise), at the heel of the stock. I find some shooters basing their ring height solely on how the bell of the scope clears the barrel or scope bases and not on the most comfortable eye position.