There is no "right" answer. When doing a single painting, I make layers as needed and only as needed. And I juggle the sorting in the way it looks best -- as I go. I tweak and seek out my next move because the painting lets you know, or at least suggests ideas. Believe me, you'll know when that last move didn't work. Think of it as a conversation between you and the painting.
A way to kill your creativity is to try to paint a painting all the way through to the end before you even start. It very rarely follows that course. And if you're going for what looks best, wait till you see what looks best in the moment. That then dictates your next step.
And as mentioned, you develop a general idea of how to go about something. AND, this is important, you could find yourself wondering what would happen if I did (X Y and Z)? And because it's present in your mind, you simply try it. It works or it doesn't. If it doesn't you back up and try something else.
The beauty of digital painting is that you're free as your imagination and your logic moves you. And you keep the methods you like and dump the ones that didn't work. But don't get trapped in mechanics if you can help it because it takes you away from what you're doing. Your method will develop through the doing.
Look at what kids do when they get onto the computer, how come they just fly when old geezers are locked in dread of looking stupid or being wrong? It's because kids don't ruminate. They just get in there and play without fetters. All the finesse comes later from experience, which is the best way.
Having said that, there are tons of tutorials for getting started here and on YouTube and Deviant Art etc. Those can be very helpful if you want to learn where the basics like menus are and so forth. And when you are using the program, when you hit a snag, then you can look up that one sticking point, and get back to painting and breezing through.
Just my thoughts on it. I was never one to use the manuals until after I had played a while, and then only to skim for ideas.
Have fun!
"Not a bit is wasted and the best is yet to come. . ." -- remembered from a dream