A Putting Triangle is formed when you place
your hands on your putter at address.
At the heart of a good putting stroke is the maintenance of the angles set by your shoulders, arms, wrists, and hands until contact is made with the ball.
If you face a mirror, you will see this natural triangle (see picture opposite).
Maintaining the shape of this triangle is important to your putting stroke. If this triangle breaks down in your backstroke it will be more difficult for you to square the putterface through the contact area.
The advice to keep your putter low to the ground is poor advice as it changes the shape of the triangle. You should allow your putter to rise naturally in an arc as your backstroke progresses.
In the forward stroke you should hold the triangle keeping the putterface square to your aimline until the ball has completed at least 6 inches of its roll.
Your head should be aligned in such a way that your eye-line is level. In other words, if you were wearing glasses the upper rim of your glasses would be horizontal to the ground and parallel with your aimline.
In your putting setup you don't want to do that. You should keep your shoulders as level as possible. The easiest way to do this is to place your hands on your putter so they are directly opposite each other.
Some teachers recommend: Tuck your elbows into your rib cage to gain greater control over your putting stroke. This is similar to the advice of keeping your elbows close to your body in the full swing.
Occasionally you will see golfers with one or both elbows pushed out from their side and pointing parallel to their aimline. I believe that this is a band-aid solution and would not recommend it.