So much of putting is about fundamentals. One of the fundamentals that is missed in the setup is where your eyes are aimed. Where your eyes are aimed has a great influence on how your putter head swings. Another big thing that a lot of amateur golfers do is look at the hole instead of getting your eyes back over the top of the ball. This makes it hard to get that path that the putter has to swing on.
I like to use this eyeline golf mirror. It’s simple because when you stand over it, you should be able to see that your eyes are in that mirror. There are also these nice lines on it that help you see where your eyes are pointing. You want your eyes to be lined up with that black line, which means it’s parallel to the line. This promotes a nice, good ark to the putter and you’re going to find that you swing that putter down the line a lot better and hit more putts on line.