Mount the scope on the gun for the position you will shoot most (standing, Sitting etc.) bring it up with a good cheek weld and without adjusting your head front to rear, you are looking to see a nice clean picture thru the scope. You will need to move the scope fore or aft until all you see is a clear picture thru the scope. No haze around the edges. Most scopes are in the 2-3/4 to 3-3/4" eye relief range unless you have a scout or shotgun / bow type then the eye relief is longer. Make sure you have the crosshairs level and keep the mounts tight.
they are fin to knock over cans with and shooting eggs is fun too.
I never cared for a scope on a break barrel air rifle as it seems that by moving the barrel and locking it back up there would be no way to get the barrel in the same exact position 100% of the time. I am sure it works but I just use open sights on them as I am only shooting 15 to 20 yds anyway.