What you want to do is watch the line from your ball to the putt and see how fast the dots are crossing it and which way they are going. The faster the dots, the more it will break.
In Scott's example you would aim to the right of the pin because the dots are moving to the left. How much you aim depends on how fast they're moving. Those are moving pretty slow so you only move the aim a little bit. This is where the practice comes in. With mulligans you can take that putt over and over to see what works.