A symmetrical version of the Figure Eight pattern.
Take all three balls & hold two in one hand & one in the other. Start juggling Two in one hand in a columns pattern, so that you have each ball being thrown & caught in two columns one on the inside & one on the outside. Juggle for a bit then throw the inside ball as a cascade throw over to the other hand. When the cascade throw peaks throw the third ball straight up on the outside & go into two in one hand columns on the other side. Juggle two in the other hand for a bit then make another cascade throw of the inside ball back to the starting hand.
Practise switching from hand to hand in this way. Reduce the number of throws you make before switching the two in one hand juggle to the other side. Count the number of times you throw the outside ball of each two in one hand juggle, start by throwing it three times then make the next throw of the inside ball a cascade throw to the other side. Then go down to two & then finally one. When you get this far the centre ball is thrown back & forth between the two hands. This is the base for the Double eight pattern.
While doing this pattern notice that all the work is done on one side at a time while the other hand stays idle. Instead of holding this hand still you are going to do a carry in a figure eight around the other balls.
As soon as you catch one of the vertical balls carry it over the cascade ball as it falls into the other hand & under the other vertical throw as it peaks. Bring it back over the top of the vertical ball as it starts to fall & underneath the cascade ball before throwing the ball you've been carrying straight up on the outside. Then practise the carry on the other side, each time returning to the base pattern. Keep practising & gradually work up to making a figure of eight carry every time you catch one of the outside balls.
As with all carrying tricks, carry each ball by gripping it between your thumb, fore & middle fingers to present as much of the ball to the audience as possible. Also relax your wrist & make it bend & twist with the path of the carry.
Once you can do this trick you may want to learn the 423 Orbit pattern which uses the same base pattern but involves a different carry.