Always make sure you buy the correct size mount for the scope rail.
Mount a bipod or gun rest if possible, put a level on your breach block, level it DO NOT MOVE IT.
Then fit the scope mounts, make sure they level up with the breach block, once this is done put scope on without moving the rifle so everything is still level, then place a plumb bob 15 yards away, parallax the scope for 15 yards so nice clear picture and centre the scope reticle to the line.
Once that is done secure scope down evenly ...
Adjust ocular lense (nearer to you), but setting px on infinity , and look at the sky or