This is a public service announcement: Make sure there is nothing breakable in the room if you're indoors, or that you are away from trees, ponds, roads & overhead telephone/power cables if you are outside. Thankyou.
To start with practise throwing one ball higher than normal. To throw higher you will have to use more arm movement, don't bend your wrist, keep it in line with your forearm. Let go of the ball when your arm is horizontal. Let go too soon & you'll throw away from you, too late & you'll chuck it behind. Just practice with one ball, work up from the normal Three ball cascade height & get higher & higher. Always catch with the opposite hand. Throw so that the ball comes down where you can catch it without having to take a step or even reaching out your arm. Don't worry about lack of space if you're indoors, ceiling level is the perfect height for the next trick, a three ball flash. Practise until you can consistently throw to the ceiling.
Now put a high throw into your cascade. Try one at a time, then the same ball each time, then every right, then every left & finally every ball (this last one is also known as high cascade, slow cascade & 522 (which is siteswap notation)). Remember to wait for the ball to peak, you'll have to wait longer the higher you throw. When juggling a high cascade put your head up & fix your gaze on the peaks of your throws. You should still have a nice even rhythm, but it should be much slower 'throw....throw....throw....throw....'