Faced with a sloping approach putt, draw line from the ball directly to the hole, ignoring the slope.

Now, when you hit the putt, make sure the ball does not cross that line before it gets to the hole. If the ball does cross the line, it will never go in.

You will make more of those putts by following this rule, and if you miss, it will be on the high side. The leave will be shorter than if you missed on the low side.