Here's something of an example of how I do these cartoons paintings.
Make a new 8x10 RGB file. I use a rolled rag brush to make a background.
Then I rough in the character on a new layer.
Next I make another layer above the rough and add some color, thinking about the highlights and shadows.
Finally I clean up the edges some of the rough and merge those two layers. Then its just a matter of filling it in. I scaled him down to make him look smaller and adjusted the background. Added the linear light texture layer and call it done.