Raise your score at the range and impress everyone.
Breath, this is the biggest part of shooting a rifle: Control your breathing. Ideally you want to get your cross hair or sight near what you want you want to shoot, then you want to hold your breath, zero in, and fire. A good amount of time to take holding your breath is 10 seconds, although it may take you longer depending on what you are shooting and certain circumstances. If you are using iron sights, then make sure the rear and front sight are lined up correctly before shooting.
Push the butt of the gun into your shoulder: You want to make sure that the gun is lodged tight against your shoulder. This makes you slightly more shaky, but you have substantially less recoil, and your shoulder remains intact and bruise free (if you have a higher caliber rifle, this is a must.) Doing this has prevented many a bruise.
Don't use your entire finger on the trigger: You want only the tip of your finger on the trigger to prevent moving the gun as you shoot. And don't forget, for safety's sake, keep your finger away from the trigger until you are ready to shoot.
Regularly clean and maintenance your rifle: This is very important as muzzle and barrel obstructions can throw a bullet way off. The big things to check for are obstructions at the muzzle, flash suppressor (is there is one), and in the rifling. Do this after you shoot every time, and make sure you do full cleans every couple weeks.
Purchase a lighter trigger: Most guns ,from the factory, have a very heavy trigger pull. This is prevalent in a lot of assault rifles especially. If you want to make your shots more accurate, you can lighten the trigger. Look out though, if you make your trigger pull too light, then it can be VERY dangerous and may even be illegal. Note that I can not be held responsible for any injuries you or anyone around you sustains by lightening a trigger.