One of the most common faults that I get asked to solve is how to stop the putter wavering around on the back-stroke. Often players find they can't take the putter back smoothly, and find it difficult to start their back-stroke.
The first thing to check is your grip pressure. If you're gripping too hard you'll take the putter back with your hands, and find it difficult to use your shoulders.
Feel as if you can't grip the putter any lighter, that if you do it will fall out of your hands. Immediately you should feel the shoulders doing more work and experience a less jerky stroke.
Also try to hover the putter at address, don't ground it. This will again encourage a smooth take-away.
Simon Iliffe is head professional at Bramley Golf Club, Surrey. www.theshortgame.co.uk