You learn to keep the balance up "playing" your brakes AND body, too. It's not necessary to block the bike: you have to feel which way it wants to move. When you turn your handlebar aside, the bike will try to move back, so you have to push a pedal slightly stronger than just putting your foot on it. Also, when the bike is about to collapse - use the brake not to lose it. It's all about practice actually, you should be doing well in a few days if you train according to the video posted above. Good luck.