Remove the scope from its current mounting. If not currently mounted, move to step 2.
Refer to the instructions on your scope mounting kit, and install the base and rings on the rifle. Installation instructions will differ based on rifle type and manufacturer.
Place the scope as far forward in the mounting hardware as possible while holding your rifle as you would normally shoot.
Move the scope towards your eye slowly, until you have a full field-of-view. This position should be between 3 and 5 inches from the eye. Keep the scope in this position.
Rotate the scope to place the elevation dial at the top of the scope.
Ensure that the vertical reticule of the scope and the vertical axis of the rifle align, then tighten the ring screws.