*LARGE FILE WARNING*
I'm not sure who this will be useful to but I figured I'd do one of these anyway. I guess if nothing else it gives you a rough idea of my process.
[A] Here I have the linework, which in this case I drew entirely in PS, nothing exciting here yet.
[B] What I've done here is I've locked the line art layer and set the blending mode to "linear burn", this is how I achieve my color holds.
[C] Here I apply the "flat" colors, probably the most tedious and un-enjoyable part of the the whole process.
[D] This is where it starts to get fun, here I apply cel style shadows with a deep blue or purple.
[E] Now I add some highlights and gradients. With the highlights I set the layer blending mode to overlay and use white or a light grey.
[F] At this stage I want to give my shadows more of an authentic "animated" cel look, so I duplicate my shadow layer and apply a gaussian blur of about 7-9% whatever or whatever feels/looks appropriate at the time.
[G]Another fun part, applying some mood lighting. What I do is I select my shadow layer (CMD+Click), then Invert (CMD + i) Then while your selection is still active click on your flats layer, select the magic wand and (option + click) OUTSIDE of the flat colors, this will deselect everything exept the selection you need to make your lighting, while the selection is still active create a new layer over or under the lineart (over is probably better) and fill or use the gradient tool to cast some lighting, use a bright color. I'll bet none of that made sense lol *sigh*
[F] Here I add a few more effects, blurs and such. To bring out more color I'll flatten everything, duplicate the layer, set the duplicate layer blending mode to HARD LIGHT, 50% opacity and apply a noise filter. FILTER>ADD NOISE>MONOCHROMATIC (set values to whatever suits you, then apply a Gaussian blur of about 40%, all of this together should give the image more color and a smooth animated look. Also you can play with color adjustment to intensify the mood of the image.
I hope that made sense to somebody lol
Never done one of these so there's plenty of room for improvement lol. Perhaps my next "tutorial" will be my approach to anatomy construction and posing.