Putting, generally speaking is 50% of the game. There are many styles of putters, ball placement whether front or back foot, putting really comes down to comfort. All good putters have a few things in common. Their hands work together, the putter face is square to the target, the ball is stroked not on the toe or heel but in the center and the player gets the ball to the hole. Rarely do they leave putts short under the premise short putts have zero chance to drop in the hole.
Whether practicing or before tee off, get to the practice green. Start out with making ten 3 foot putts in a row from the same spot. Choose a flat level area with no break or undulation. If you miss, start over, make ten even challenge yourself to make more. 
However just don’t step up to the ball and start putting away. Work on those things mentioned that all good putters have in common with every putt you make.
Now move 4 feet away making five in a row. Don’t quit, make five in a row. Once the player has done that, step back to about 6 to 8 feet. From here putt about 10 balls making what you can. Take mental notes on those putts that did not go in the hole. Where they short, left or right of the hole looking for a pattern. If consistently missing to one side on a flat surface, odds are putter is not square to the hole. If consistently short, practice getting the ball just past the hole.
