Superfast shading tutorial

Lineart from [link], help for [link]
My brush settings: as big as fits in the space I'm shading, normal boring round, 5-12% opacity (24ish% for darker areas), transfer and size changing on.
The pale arrow in the upper left is pointing toward the light source

Just a little thing. What my scrawl says, basically:
More saturated = more reflected light
I like more than one color in my shading
don't shade with black, pick a slightly different hue (haha, not really, but I forgot to put it in there... when I used to cellshade I used a dark, desaturated purpleblue)
Think in 3-d shapes. Light is rays; if something's in the way of the ray, there's no highlight there! Shadow is the natural state of existence; if something's not lit by the light source or reflected light... it's dark.
Adding a little shadow to bits of the background partially obscured by the foreground is a good way to draw attention to the foreground. You can also do that in reverse.

Things I didn't cover: Backlight (It's the same process! Just put the lightsource behind the object your shading, and if a given point can't 'see' the light source... don't put light there!) translucent stuff like the edge of a mass of hair or fur (IMHO that's what layer transparency was invented for; put it down slightly, Add a tint of the light source color, more for more extreme, erase on low opacity [argh term confusion] if it's transparent in places, bam, done. Works pretty well for leaves too.)
I don't know what rim light is. I have the strong suspicion it's a theoretical fallacy but I might be wrong.
I've been learning to shade my whole artistic career, but [link] has been particularly helpful! It's mostly geared toward painters, but I think you could adapt some of the advice to more cell-shading like styles too. The color commentary in the corner is how I've been shading skin lately; any of the three from [link] are a better reflection of how that should actually. Just threw it in for fun
Hopefully some of that was useful; I'm still recovering from hurricane then power outage then 9 hours sleep total over the course of two days so I tend to blather on and get really offtopic...