Mine's not exciting. I typically have one shade layer that sits above the base colors but under the highlight layer. I DON'T have it set to 100% opacity to start, because I've found that if I do this, I end up leaving the layer and not realizing it and shading on the ink or base color layer by mistake.
I set it to 30% opacity, select where I want with the selection tools (usually the magic wand because it's fastest), and define the shaded area with the pen tool. Then flood fill. If I feel like it, sometimes I'll just draw in the area without selecting, but it's usually easier/faster for me to select.
I think I'm usually pretty good about keeping the light source in mind. Sometimes I throw myself for a loop though; since my main character uses electric powers, sometimes he is
the light source, haha. But I mostly try to use the shading to define shapes and make them appear more 3D I guess. For the most part at the moment, my areas have overhead lighting, so I tend to just roll with that. I do have these pages
though where the only light source in the room is a meager red light on the camera. But I decided I wanted the shapes to be defined, so I still emphasized them with my shading.
I also try to remember that characters will cast shadows, and the shadows will look different based on the light source's location and other things. It's kind of easy to forget though.
I really hate shading my comic. I was trying to do the weird hatching thing at the start so I wouldn't have to shade, but I got enough comments on it that I switched. Now I just angrily grumble to myself every time I start shading.
As far as coloring goes, I don't really enjoy doing it in Manga Studio, but I love
it in Paint Tool SAI. Manga Studio isn't bad, it's just Paint Tool SAI is WONDERFUL and it makes me sad to not use it, haha. I don't like using more than one program to do my pictures though, since if I need to correct a mistake, it becomes very tedious/annoying to correct it in the first program and send it back to the second one (where I'm likely to find ANOTHER mistake).
I shade my comic differently than I do for stand alone art. My comic uses just black, but I like to mix colors for shading
. It just adds too much time to each page to shade that way.
So... yeah. There's a lot of different ways I shade and the one I hate the most I use for my comic. I'll probably change my style eventually but I need to figure out how to speed up my line art first.