Remember that when you first hit the ball it will tend to go straighter as it is rolling faster. As the ball slows down the ball will be affected more by the slope/curve of the green. Get the ball started on the line you want and expect greater changes at the end of it’s run.

Besides reading greens you also have to know your distance. Use the same tempo for every putt and change the length of the swing to adjust the distance. Practice putting by swinging the putter from one instep to the other and see the distance. Then from the outside of one foot to the other and see the distance. This way you can better judge where your ball will end up.