i'm practicing with a method where you only paint space first. with a big flat brush or the free selection tool, which in my opinion is perfect for this task, i just paint the silhouettes of the subject i have in my mind. i keep each part of the character separated on different layers, that will ease the painting process.
the second step is about painting details inside these shapes. to do so, i use the clipping mask tool with flat or simple textured brushes. i think the whole thing would work even better if painted as realistic as possible.
that's it, nothing much more about it. the cool thing about this method is the resulting contrast between simple shapes and the fine details painted inside them. also it's something that allows you to get faster results since we're practically omitting the sketching process.