I missed my flight out of CMH around 10 years ago and found this book (that came with three balls) in the airport with a couple hours to kill. I remember the first instruction was something like:
Hold the three balls in your hands. Now, drop them. Get used to this.
Was happily juggling by the time I boarded the flight.
Keeping them in that plane is the biggest hurdle to get over for a lot of people. Try juggling in front of a wall. Or standing over a desk against a wall (no chasing drops). You can even keep juggling bounces off the wall. Also, lots of practice with just two balls doing the exchange.
I remember barely getting through the instructions when a lightbulb went off, I said, "oh!", and immediately started juggling. That book explained it so simply. Before that, juggling seemed to be some sort of dark art requiring amazing dexterity.