Begin with a Bore Sight
In the old days, you did one of two things first:
A.) You would mount your scope, remove the bolt from your rifle, and look down the bore, trying to match the sight picture through your barrel and scope. Every once in a while, it worked shockingly well, sometimes not.
B.) You’d simply start launching lead at a pie plate at 50 yards. If you were lucky, you’d hit somewhere near the plate. If not, you’d have to allow the guess and check method play out, burning through as much ammo as it took in the process.
Today, you can ensure that you’re rifle is hitting paper with the first shot using a bore sight. These laser tools are not exactly precision instruments and they’re not intended as a replacement for “zeroing in.”