When starting/stopping, it helps to sit up, vertical. This gives you a similar balance to an ordinary upright. Start with one pedal at slightly before 12 o'clock, give it smooth, firm push with your dominant leg, then relax, sit back and raise the opposite leg. Flintstoning will not give you enough momentum to get a good start. Practice starting and stopping on a flat open area like an empty parking lot, as others have suggested. Just like a regular bike, once you get rolling, the balance is easy. Next, practice slow tight turns. Keep in mind that you need to let the bike tilt into the turn, just like an upright. If you lean with the bike, you will oversteer and lose balance. Think of letting the back of the seat slip from behind you as you turn. If you want to turn very tight and very slow, sit up vertical like starting/stopping. When you are comfortable on the flat, practice starting/stopping on slight inclines. Soon you'll find that you can make smooth, clean starts even uphill. Once I learned to let the bike "slip and tilt" under me in turns, it was as if I became one with the bike. Don't even consider clipping-in until you are completely comfortable. Personally, I recommend mountain bike pedals with pins. They provide excellent grip without being locked to the pedals. Soon you'll be having more fun than even.
