I would make a background layer and then make three color layers, and on top of them, a line layer, and at the very top the lines that seperate scenes.
Use the first color layer to make the main color.
Use the second color layer for markings.
Use the third for shading and highlights if you use shading and highlights.
If you make a color mistake, turn on lack alpha on the layer you want to edit and then just change the color! No need to erase or redraw!
Make sure the line layer is over the color ones and then it is easier not to go outside the lines.
For background I would start by useing paint bucket for the main color and airbrush for extras.
For lines check out the smoothing feature, this really helps!
For spotted pattern turn on lock alpha so that they don't go out the lines, turn the size to 1-3 and turn on scattering!
Smudge is useful to make certain lines less noticable if you want.
And that is all the tips I can think of right now! Hope it helps
