A common problem I see with my students is poor technique when addressing the ball on the greens. This leads to bad alignment causing missed short putts and three putts. If the putter face is not correctly aimed, you have little or no chance to start your ball on the right line. How do we fix this? The solution is easier than you think.
Once you have read your putt, it is very important to address the ball correctly. The most consistent method I have found is to step in with your right foot first and only your right hand on the grip (pictured above). In this position you are keeping your body open to the target and your head and eyes up, checking the alignment of the putter face. Once you feel you have your putter aimed correctly, step in with the left foot and situate both hands on the grip.
It is VERY IMPORTANT to keep your eyes up at the target while adjusting your feet. When your eyes are focused on the ball during setup you are aligning yourself using a memory of where you think the correct line is. When this happens, most golfers will tend to align their body to the right, which shifts the aim of the putter right as well.
Throughout the setup process your eyes should be moving back and forth from the ball to the target. Look at some of the best putters in the world Steve Stricker and Jordan Spieth. They will look at the hole/target many times to insure proper alignment before making their stroke. I hope these simple instructions will improve your alignment and help you make more putts!