Dominant Eye or Master Eye
No matter if you are shooting a rifle, shotgun or handgun, you will first need to determine your dominant or master eye. The "dominant eye" is the eye you use for sighting purposes. The dominant eye is the stronger of your two eyes. The dominant eye will judge speed and range, and focus more accurately than your other eye.
Most right-handed people are right-eye dominant. Most left-handed people are left-eye dominant. Some people are cross-dominant. They are right-handed, but left-eye dominant. If you are cross-dominant, your instructor may wish you to mount the rifle or shotgun on your left shoulder instead of the right shoulder. This can make the difference between hitting or missing the target. Firearm instructors have other options for helping individuals who are cross-dominant.