We all get nervous on those tricky 4-foot putts to save a par and tend to jab at them or try to steer them into the hole. We also tend to stop or decelerate at impact. This will never produce a solid, smooth roll on the ball.
A great thought you can have is what I call, "The Flashlight."
Imagine that your putter is a 3-foot long flashlight and the ray of light is shining out the bottom of the putter. Once you’ve established the line of your putt it will now be your job to, ‘shine the light’ at the target. If you think of shining the light through to the spot you’re aiming at you’ll swing through the ball and will accelerate through the impact zone with a much smoother stroke. Instead of thinking ‘hit’ the ball, you’re now thinking of shining the light. For those golfers with the "yips" this can cure them as well. On a breaking putt you would shine your light to the high spot of the break, where on a straight putt you’d shine your light right at the hole.
On longer putts the flashlight can also help you gauge your speed better too. On a 20-footer your flashlight will come up and shine toward the hole. On a 40-footer your flashlight would have to follow through a bit more in order to shine the light hole high since it’s farther away.
Lastly, since you’re going to be following through a bit longer, make sure your backswing is a bit shorter. Most golfers take too long of a backswing and that forces them to stop the putter and not follow through. With a nice compact backswing you’re now free to shine the light and watch your putts start dropping in a lot more often.