This is not so different from just juggling 3 clubs on the line. Same principle, it is easier with just one foot on the line so we can use the other one for balancing. The balance is similar but with one extra limitation. You cannot move much your upper body, or the ball will fall. Always have your core in tension and try to balance from there. Of course the free leg helps a lot too, but try not to rely on it too much.
Of course a prerequisite is to be able to spin a ball on a finger for a few seconds. There are many tutorials on this on youtube.
To start with it is much easier to use a ball quite deflated so it is easier to catch and to place on the mouth stick.
For the mouth stick I use a regular metal table spoon and add a tip on top. The good thing about the metal spoon is that you can easily adjust the angle and it holds it. The tip I use is one for Chinese plates I bought in a juggling store, but you can use anything which is rounded and smooth. I saw some people using the mini jack from some headphones. I introduce a wooden stick in the tip and then tape the wooden stick and the spoon. Then, you will need some cushion for the mouth so it is not so hard to bite. I use some cardboard or cork sheet but I am still experimenting. Then all can be joint with sticky tape or similar. I have seen some people using a wooden spoon and sanding the tip so it is rounded and smooth.
An intermediate step can be to place a Chinese plate on the mouth stick instead of a ball. This is easier to start with and also it spins for much longer (1-2 mins easily). Once spinning the plate on the line feels easy, try adding the 3 clubs. Then try just spinning the ball while on the line and placing the ball on the spoon. When you can hold this for a few seconds, then try adding the 3 clubs juggling. The ball feels much nicer than the chinese plate and also it is better for doing it outdoors. The chinese plate is very sensitive to the wind so the slightest breeze will ruin the trick. But the Chinese plate is much easier so it is a good starting point and it looks nice too.
BALANCE AND JUGGLING 