How to Read a Green
Main points for green reading:
Clock face entry point
Visualize the hole as a clock face with 6 o'clock always in a direct line between your ball and the center of the hole. Putts that break to the right will generally enter the hole between 9 and 6 o'clock. Putts that break to the left will generally enter the hole between 3 and 6 o'clock. Be specific about what time the ball will enter the hole based on the slope.
2 ways to choose the start line:
The 'time' the ball will enter the hole is not the aim line unless it is a straight putt at 6 o'clock. Having established the entry point make sure you aim the putter face high enough up the slope so it will not miss low of the entry point. This will ensure the ball is breaking toward the entry point as it loses speed and not away from it.
Imagine rolling a straight putt to the hole at 6 o'clock with the correct speed to hole it. Whatever distance the ball would Miss low is the distance you must aim the putter on the high side. For example if you think the ball will miss 3 inches on the low side of the hole, your aim point will be 3 inches to the high side of the hole.