Many players have trouble aligning their eyes properly over putts. They may think they are aligned straight when in fact they are actually aligned left or right. This can throw off your putting stroke in a big way.
Your putting stroke tends to follow the line of your eyes. If your eyes are aligned to the left, you'll tend to pull the ball, or your putter will go back outside shut and come back inside to the left and open, which can lead to some cut puts, or putts that spin from left to right. If your eyes are aligned to the right, you'll tend to push the ball, and you will also notice that your putter may have a tendency to start to the inside and fan open, causing you to have to use your hands a great deal to square it on the way through. Neither one of these situations is good for consistent putting.
Here's a simple way to straighten out your stroke. Pull your cap brim down just a little bit over your eyes. Just pull it down a little bit tighter. As you glance up you'll see the brim of your cap, and that can be used as an eye alignment aid. First set your putter behind the ball, aligned with the target. Then set up so that the brim of your cap follows the line that the putter defined at setup. As you glance at the brim of your cap and it's running in a parallel line to where you want to start the golf ball, your eye alignment is in pretty good shape.
Now that you know your eyes are aligned where the putter is aimed, you'll be more likely to make an on-line stroke. If you putt with your feet perfectly square to the target line it's even better, because that way you have a secondary check for your eyes. Just line up your cap brim with your feet as well as the line that you are going to putt the ball on, as defined by your putter at setup.
Do this for awhile. It may feel uncomfortable at first, but it will definitely straighten out your stroke, leading to more made putts.
