Sight in your rifle before every hunting season. Scopes and mounts may look solid but they are actually fairly sensitive pieces of equipment: a single rough bump to the scope can offset your sights. Let alone if you dropped your rifle at any point last year (always be gentle with your firearms).
The first thing you need to know about sighting in a rifle is that you need to shoot off a bench or something that keeps the gun extremely stable such as sand bags on a table. No matter how still you think you can hold your rifle, you’re not a robot. You breathe, your heart pumps, you blink, your arms get tired. It’s amazing how wobbly you feel when you’re peering down a scope at 9x power while standing.
After you have fired three shots, look at how they are grouped on the paper target. Are your three shots nice and close together? If they are, your rifle is sighted in. If they aren’t, adjust your scope or shooting technique and keep repeating the process until you have a relatively tight group.
If you are still having trouble getting a tight grouping, you may need get a technician to re-install your scope or adjust the mounting. Or maybe you just need a new scope or rifle.
Bonus tip: Some experienced hunters like to sight in their rifle so it is roughly 2 inches high on a 100 yard target. This ensures that at 200 yards, your shot will be dead on, and at 250+ yards (very difficult shot) the drop will be negligible. So if you notice your shots are an inch or two high at 100 yards, don’t fret about it, just remember to not aim high. A great majority of missed shots go over the animal.