So, I have decided to make a small shading sheet for my friend on amino, to help him understand how can shading affect a piece. With the help of my mascot of course.
Shading can bring out so much depth, character, emotion, etc. So you shouldn't be stingy with it. Don't just put a big blob on the back of the character and call it a day. It looks lazy and unnatural.
While putting shading on the back of a certain body part without really shaping it looks more natural, it's still not quite there. It doesn't bring out much depth. But if you want to get some nice shading really quick, then you can definitely go that route!
As for the last way to shade, it looks more natural, and really brings out the depth and details. The good example is the shading around the mouth and eye. It helps bring out the smile of Yak, and it also makes him look like he is squinting, only adding to the mischievous factor. However, you need to be careful with eyes and teeth when doing shading that is very contrasting. That kind of shading might make the character look like they are missing teeth, and it might slightly change the eye shape. Personally, when I do the kind of shading that you see on this picture, I usually don't shade the teeth.
These rules don't only apply to the shading with a hard brush. It also applies to soft shading as well. So, keep that in mind!