What a bargain! Retailing for 99 cents, those plastic stencils that help you draw a straight line around your ball (photo, left) are dollar-for-dollar one of the most effective training aids on the market.
Aligning the mark to your starting line and the putter to the mark is a foolproof way to square the face in relation to where you're aimed. But why stop there? I have my students draw a line, then shift the tool ever so slightly to draw another line right next to it, and then keep shifting and marking until the line is a quarter-inch thick.
Why? The fatter line makes it even easier to aim the putter, filling you with confidence as you stand over the ball. This works so well, it should be illegal. Take advantage while you can!