Let me stress that the simple one-ball throw is VERY important to learn. It seems silly, but you need to spend hours just tossing one ball back and forth. You need to be able to toss it in a very symmetric scoop-toss without using your eyes. You should be able to watch TV without dropping the one ball. Infact, doing one ball with your eyes closed is the true test. This sets the foundation from which your whole juggling experience will grow from. If you put enough time into this, everything else will be much simpler.
The reason is that when you get the one ball perfected, then as you add others balls you won’t have to worry about accidentally throwing a ball too far, too short, too forward, etc which will mess up your pattern and cause you to drop the next 2 balls.
Also, when you are learning the toss, it is important that you toss sideways, not up. Your hands should be catching at 9-10 o’clock (left hand) and 2-3 o’clock (right) and releasing at 5-4 o’clock (left) and 7-8 o’clock (right). If your hands are going between 6 and 12 o’clock, up and down, then you will limit yourself for future tricks. side to side is a more stable toss with less opportunities for mistakes.