One of the most basic set-up fundamentals for putting is your eyeline. You should address the putt so that your eyes can look directly down at the ball. With your eyes positioned over the ball you'll be able to read the break of slope of the putt a lot easier and you'll be in the perfect position to make a smooth, wrist-free putting stroke.
A simple way to check your eyeline is to address the putt and then hold a golf ball between your eyes and then let it drop to the ground. It should hit the golf ball beneath you. If it misses either above or below the ball move a touch closer or further away to reposition your eyes at address.