…a particular way to putt, with two rather unusual aspects (it works for the author and maybe for you):
For address, bend over as far as possible without causing long term back pain.
Let the putter-arm system hang by gravity in such a way that the club head is on a vertical plane through the eyes, mainly by adjusting the distance of the hands from the hips. If the arms-club system are hanging by gravity, then this system can be more easily swung in a vertical plane.
Keep the wrists fixed in relation to the arms.
Keep the elbow angles fixed.
Position the ball under the leading eye.
Pull the shoulders down to the torso to stabilize shoulder height on the torso; this will keep the club face more square, but it will not impede the gravity hang of the arms which can still hang freely.
Keep the club head over the putting line during the stroke. In other words, move it in a vertical plane. This requires that the arms move outward from the body a little on the backstroke and followthrough, but they are still hanging by gravity (test it by stopping mid-stroke).
Let your head turn with your torso (we know this is unusual, but it reduces the difficulty of the swing and concentrates the mind on the torso and shoulder area, and away from the neck. Brain power is wasted while keeping the head from turning).
Watch the clubhead during the stroke (give it a try); your eyes should move a little in their sockets to do this, (if you are using shoulder movement to swing the club, as is normal). Watching the clubhead during the stroke will provide cues to your nervous system and keep the stroke smooth. It also shows you the direction and length of your stroke, improving control.
Practice aiming and stroking separately, then together.
Use the same brand of ball on a regular basis, or use different brands of balls tested for bounce height so they all bounce to the same height. Test balls by dropping them (the reference ball and the tested ball next to each other) on the same spot on the same floor from the same height. Keep a reference ball for this purpose.
The Swing (non-putting swings)
1. We point out something missing from swing technique. Our little “secret:” Let your body move forward on the backswing and then backward on the downswing, then forward on the followthrough. Soft ankles help with this. Do not prevent yourself from moving forward on the backswing. You might be tempted to push down with your toes to prevent forward movement on the backswing, but this is dangerous. (Forward means the direction you would go if you were to start walking straight ahead from the address position.) Forward movement is a natural reaction to swinging a club or any weight around you, and if you resist it you will be in a very difficult position. It will be hard to impossible to get back to hitting position by impact. Rory McIlroy and many others allow this sway movement. You can see it on video here; the first example is about 35 seconds in, and another at one minute 40 seconds, among others. The head moves forward on the backswing, backward on the downswing, and forward again on the followthrough (very quickly on the downswing so it is a little hard to see). It is more prominent on the longer clubs because they use flatter swings.
2. Don’t “move off the ball” (to the trailing side) on the backswing. Moving to the trailing side again makes it very difficult to get back into the hitting position, requiring a lot of leg work and timing. If you don’t move off the ball, less physical effort and physical coordination is required, so the swing is more consistent. To learn to stay centered, put your feet together, then pose in various positions of the swing, keeping the weight on each foot the same.
3. Check to make sure that the backswing starts tangent to the target line.