A good way to practice this is to randomly skate up to objects (both high and low) and try to stall on them. As you get more practice, your body begins to learn what it needs to do to jump that high and stall in the proper position.
Approach the bar/curb slowly, taking care to run perfectly parallel to it, and be slightly to one side. As you near the bar, jump up nice and high and turn 90 degrees while watching your landing spot. Watching where you will be landing is essential to success. Spread your legs about shoulder width apart, and absorb the impact in your knees.
A couple of key things to remember are your landing and your stance. When you land, you must be sure to land between your tiny middle wheels. Otherwise you will catch on your wheels and you will go flying. Your stance is also very important. Think of yourself as trying to stand on a tightrope- Its hard, but possible. Try and stand erect, with your arms stuck out for balance. When you try to correct a mistake, adjust using your hips and arms, and not your knees.
