To promote a stable face at impact when putting, as well as any other shot, your grip needs to be secure and correct and your body needs to be in balance. Although a putt may not be the biggest swing you bring to your golf game it still needs to be correct. What is correct? One that gives you a good feel for different lengths of putts and allows you to return the putter head back to a square position at impact. If one or both are missing, you need to change grip style, pressure or configuration. If you have problems with your head moving in the putting stroke, or have issues hitting the sweet spot consistently, these are telltale signs of swaying or off balance motions during the stroke.
For more information or help with these items, please see your local PGA golf instructor.