The Chalk Line
This drill will help you with the most basic fundamentals in putting. You will be able to check your alignment with the putter face and also check your path both backstroke and fowardstroke.
Find a straight putt and sprinkle the chalk line from 6ft and in. Place the ball near the start of the line in the middle as shown in the picture. Place your putter behind the ball as usual and check your face alignment. Once it's square stroke the putt and try and get your ball rolling along the chalk line and in the hole.