If the rifle is a bolt action I remove the bolt and bore sight it by eye to get the scope lined up with the bore. I do the same bore sight thing to get it on target. New scopes should come with the aiming point centered. On used scopes I move them from stop to stop (gently) and count the clicks to center it. If the bottom of the scope and the top of the base are both flat I use feeler gauges to level the scope. If not I just eyeball it, moving it until it looks right.