You're going to want to gather some decent speed for this one. It's not the kinda trick you can just get onto and hang out until you come off. You've got to earn it. Your front foot should be close enough to your nose that you can stick it on the ledge, but far enough back to let you pop a good ollie. Come at the ledge parellel. As you pop, you should shift your momentum so you're ollieng towards the ledge to get your nose locked in. It's almost like you're nose sliding the side of the ledge. Once you're on there, keep your front foot pushing that nose down and forward. If you stay balanced on the ledge, the dismount isn't too tricky. You kinda nollie out, and use your back foot to control the tail so you land riding straight. Make sure the ledge has a good coating of wax, especially on top where your wheels are sliding.