Need more info, like what gun are you having a problem on, brand of rings, bases, etc.
Some rifles require special rings, some rings actually have a side that must face forward, etc...
If you have the right items, & them installed right, you may simple need to lap them to correct a slight error in alignment. For anymore than a slight problem you need to return the rings & get an other set, or better yet try a different brand.
Just my 2 cents here, but some also will suggest shimming the lower base. However, for my taste this should be the last resort. Anything under a mount is an open invitation to looseness later. Hope this helps, k