>>1677283>>1677282I basically trace with the pen tool around what I want to be the solid shape in the end. Once I have my shape I make sure to name the path so it doesn't get deleted with the next work path gets made, and I convert it to a selection and fill it with the most representative color in that shape. A lot of people do gradients with certain shapes that would go well with them.
I go around and do that for everything that needs it and try not to miss anything, and eventually it works out. I can't speak for anyone who does these but myself, they might have a totally different method but that's what works the easiest and most efficiently for me.
Just make sure to keep up with naming layers as you make them or you'll end up with 25+ unnamed layers that you need to order and will need to toggle visibility for a lot.