Bars: Cast Squat-ons
Looking back to my earlier years in gymnastics, I remember the cast squat-on being a rather scary trick to learn. After all, you're trying to get both of your feet on to the bar while your hands are still on them, and you can't lean forward too much or you'll fall forwards (perhaps face-first), but if you don't lean enough, you'll fall backwards.
Luckily, though, once you've done it for a while, it gets less scary. You learn how to jump off forwards and backwards safely.
Before beginning, you should be able to do casts with a certain amount of confidence. You don't need to be able to cast to handstand, but you should at least be at horizontal at the top of your cast. You're going to need to be able to get your feet on the bar, and the higher you get, the easier it is. A good drill to work on improving your casts is simply to do several of them in a row, progressively making each one higher. Some points to remember:
The next obstacle to get over is learning to get your feet in between your hands. Sounds simple, but sometimes it's difficult to judge exactly how much you need to tuck and exactly how high you need to bring your body in order to get your feet to go where you want them. You can do a simple drill on the floor. Bend forward so that your hands are on the floor about half your body length in front of your feet. Bend your knees a little and jump, lifting your hips, and bring your feet in between your hands. If you're strong enough, you might even be able to control how fast your feet come back down and place them precisely on the imaginary line between your right and left hand.
Do you feel how high your hips had to go? How much you had to lean forward? How much you had to tuck? These are the little things you should learn to feel each time you do this, and remember them for when you try the squat-on on the bars.
When you can comfortably get your feet between your hands, stand up straight and imagine seeing the high bar in front of you.
Next, you can go ahead to try putting the two pieces together on the bars. Remember everything you did in the drills. Try to keep your feet together and avoid getting into the bad habit of trying to get one foot on before the other. It's an incredibly difficult habit to get rid of. And when you can solidly get your feet on, you can try standing up on the low bar and reach for the high bar.