Ok. Let's see.
So you've got your line art drawn? GREAT. Now color it. How? Alright, so if you're using photoshop, let's pretend you are, you need to use a multiply on top of the lineart.
|Flat colors. It's just the palette, no real shading or lighting. This part should be easy.|
Alright, so lay down your flats as a multiply. Be messy, this part if fun. If you're all conservo, then it's not fun. Fuck around and try some things.
Then you'll want to give yourself some lighting indication. Pick the direction that works for the piece and on a new layer, start painting over top of it, MESSY! Get your hands dirty. Pick the colors and paint lighter and darker versions around those patches to indicate where you want lighting to be.
|I added a layer on top of the last one (the multiply flat colors one) and started painting lights and darks.|
That's all I've got right now, but I'll go alt-tab right now and work a bit more. Doubt I will finish this on the weekend as I'm super busy, but I wanted to get started and see what happened.