I read the break backwards (from the hole to the ball). As the ball slows down, it will take more and more of the break. Where the ball is first struck, it is going at its fastest speed and the break will be the least.

I a simple 1 break putt that is at a consistant angle, imagine the ball rolling into the part of the hole that is the high side of the cup. Start to draw an imaginary curveing line from a point about 1 foot away. If there is a lot of break, then you will almost be at the top of the cup.

From there, you break the putt in half. Read the line that it would take to putt from where a streight line intersecting your ball and where the 1 foot putt would start. This will have a break of x feet. Take that distance and add half of that. That will be the amount of break the ball should take.

Example Here