Hey Cutty.
depends which rings you use.
if you have rings with 1 screw either side, or 2 screws either side.
what you have to do is try to tightend the upper part of the ring down with even clamping power on the scope tube either side, otherwise the scope has a tendency to rotate within the rings. tighten the screws doen so that the rings uppers have an equal gap between top and bottom at the possition where the screw goes through. do this until you can only just rotate the scope in the rings. level the scope of and make sure you have the correct eye relief. Then you tighten the screws down a little at a time and equaly on each screw. start on one screw and then go to the opposite side furthest away screw. ed. start front right, tighten down 1/4 turn. then go rear left, tighten 1/4 turn. then front left, 1/4. then rear right. carry on like this until you have the scope tight. for rings with multiple screws, follow the same principle but also a do the same sort of alternation per ring.
hope you follow that..
Pete