My example is not the best cascade around, this tree has plenty of flaws. But it will give you an idea of some of the things that go into making a cascade.
There is the full cascade, where the descending branch terminates below the feet of the pot, and there is the semi-cascade, where the descending branch terminates above the feet of the pot.
1. there are 2 styles of pots for cascades, both are deeper than the normal shallow bonsai pots. There is the squat pot, where the dimensions approach that of a cube, for example a 5 x 5 x 5 inch pot. It can be round also, for example 4 inches diameter, and 4 inches deep. This is the more "modern" in North America style pot for a cascade. The "older school" is these very tall narrow pots, such as in my photo, that pot is roughly 5 inches diameter by 9 inches tall. Choice of style of pot is entirely personal taste.
2, the cascading branch can actually be the apex of the trunk, as it is in my example photo. Here the apex of the tree is below the feet of the pot. The other option is to take the lowest branch and bend it down to become the cascading branch. This is pretty common also. Note that the trunk is at an angle. This is important. If the trunk were perpendicular to the soil in the pot this would really look awkward. As early as possible, next time you repot, tilt the trunk to an angle. This will help create the cascade. Think tree on a cliff over a river or lake, reaching for light. If the trunk is perpendicular to the soil in the pot, the cascade looks fake. Or forced. A nice roughly 45 degree angle visually makes sense. (does not have to be exact, actually better if it is not exact 45 degree, a little above or a little below is fine).
(Flaw) - my tree in the photo, the bend that brings the apex down is too much of a "rainbow curve". It would have been better if it had been a sharper bend. y the time I bent the branch down, it was already to woody, I was risking breaking the trunk. So I was no brave in making the bend. Also the bend is too smooth, there should have been more back & forth & left & right bends and twists to my cascade. But I work with it as it is. When this azalea blooms, there are enough flowers, you forget about the flaws.
Branches on the descending trunk should follow a left-right-front-back pattern. The "front" of the descending trunk actually faces the pot, we actually are looking at the "back" of the tree when we look at a cascade. Or sometimes the side, Depending on how you display it.
You will find the branches "above the rim" of the pot will need pruning back 2 or 3 times more often than branches "below the rim" of the pot. Keeping energy balanced is one of the real horticultural challenges in developing a cascade. It is difficult to get the same size leaves and the same density of fine branches from top to bottom. This challenge is part of the fun of creating cascades. It is a niche that has its own set of tricks.
But I am happy to see you are interested in creating a cascade. It will be a fun challenge for you.