How do you successfully read putt preview?

Putt Preview merely is a guide to how the ball will roll given the speed / slope of the green. You can always adjust the putt after you see a preview, based on how far you're out.

Nailing putting is all about practise - I'd suggest a few rounds at St Andrews, where the greens are generally large and flat, to hone your skills. While you're there, you can mess around changing the course speeds from slow-average-fast to get an idea of the differences those settings make to your putting.

Good luck!