Here's how it works if you don't know it. Pick four numbers i, j, k, and l, such that i < j < k < l. Now make 20 attempts to do i repetitions of your favorite trick. It doesn't matter if you succeed or fail, each attempt still counts towards the 20. Then make 10 attempts to do j repetitions, and then 5 attempts of k repetitions and 1 attempt of l repetitions. Do that every day. When all your attempts succeed, increase i, j, k, and l. I cheat a little and increase i, j, k, and l even if nearly all my attempts succeed. So does Matt Hall, so there.
Since last Wednesday, I have been trying this with 3 of my most frustrating juggling patterns: 5 balls, the 561 siteswap, and 3-in-one-hand. Until tonight I wasn't sure it was helping. A lot of my attempts failed, and my numbers of repetitions were disappointingly low (e.g. for 5 balls, 10, 15, 20, and 30 throws). And then tonight, out of the blue, I picked up 5 balls and juggled them for 232 throws. My previous personal best was around 150, and that was months ago!
Yippee! Practicing works!