Start w/ butter or disco box. Those are the ultra fat ones. Best is one that you can just ski onto without having to gap to it. Practice 50/50. That means going straight on the box; no 90 on. Think wide stance, but no wedge. Practice settling or getting a little lower when you are on the box. Once stance starts to feel solid, start 50/50, pivot feet to 90 and then back. If that feels good, jump up and pivot your feet like you did from 50/50. Try to land in the same solid wide stance that you had when you pivoted fro 50/50. Main keys are to keep wait evenly dispersed on both feet, settle a little to lower your center of mass. Most important, keep your dick between your feet, assuming you are a guy. If your hips cross over your uphill foot, you will go down. Sliding a box or rail is not the same as doing a hockey stop. Good luck and have fun.