Regardless of distance, you want the scope mounted level. Set the rifle up on a table or flat surface where you can look through the scope at a distance (20 yards or so)without disturbing the gun. A gun rest or vice is preferred. Get a small level ( I use a line level) and find a flat spot on the action to level the rifle. The scope cap is not level due to threads. You can use the bottom of the scope but generally you can find a place of the action or rail. Set a plumb line up where you can view it through the scope. Line up the vertical cross hair and tighten the ring screws diagonally a little at a time. Afterwards, recheck everything to make sure nothing shifted. You should be good to go. One way to verify is to do a tall target test but that's another discussion. Best of luck!