Good putters share two consistent factors in their strokes: their hands are slightly ahead of the ball at impact and they employ little or no wrist action. Bad putters tend to break, cup, or bow their wrists through the stroke, resulting in bad direction and distance.
To eliminate wrist action, find two common objects: a wristwatch and a 12-inch ruler. Put your watch on your leading wrist (the one closest to the hole). Slide the ruler through the watch band on the outside of your forearm. Take your putting stance and keep the ruler in place so that the back of your hand, wrist, and forearm stay connected to the ruler.
This drill helps to develop firm wrists, leading hands, a solid triangle (arms and shoulders) throughout the stroke, and a square clubface at impact. Use a ruler when you practice your putting and soon your opponents will be bowing down before you, King of the Carpet, Ruler of the Rug.