One of the most important fundamentals in putting is the set-up position. Set-up to the ball poorly and you'll be forced to make awkward swing compensations to roll your putts into the back of the cup.
In a perfect set-up position your eyeline should be directly over the ball. This will help you read the line of the putt far easier and will put you in the perfect posture to make a wrist-free pendulum action putting stroke.
The easy way to check your eyeline is over the ball is to address a putt and then hold a golf ball directly beneath your left eye. Let go of the ball and let it drop to the ground. If your eyeline is correct it should hit the ball you are going to putt, if your eyeline is out the ball will land above or below the golf ball. When this happens you'll need to adjust your set-up accordingly.