Go fast, roll up really close to the object, pop and turn while keeping your shoulders square. It's all about where you pop and keeping your shoulders straight.
it really is all in the shoulders.
try it on a low ledge that isn't that slick by going really fast and just powering through.
aim for the steepest lock you can get on the corner; landing in front blunt on top of the ledge can make you stick pretty bad.
you want to keep your shoulders parallel as you twist your lower body to lock in
if you learn the trick hauling ass on a not-too-waxed ledge, you don't have to worry about slipping out and will get comfortable
locking in and popping out proper. staring at this louie photo might help too