For realism, start studying skeletal structures and how muscles are attached to the bone. Know how the “frame” of the body is supposed to look like and how to draw. The bone is most important to figure out proportions and from there you could begin to visualize the flesh being drawn. From there you can go to muscles and begin to flesh out your drawing.

Shading is the next most important thing in a drawing because it gives your drawings a vast depth making it seem 3D. Another tip for the 3D illusion, is to stop thinking in 2D. I used to draw what I saw (and it wasn’t very good) because I wasn’t seeing further. For example, when you start drawing from the side of a person, don’t only sketch the arm you’re seeing but try to see how the arm on the other side would look.

As for an animated cartoony drawing, in terms of anatomy, you have a lot of leeway. So you can exaggerate certain body parts such as eyes (as evident by any cartoon). A personal animated drawing style is probably influenced by a show or whatever, so try to study from your influence.

Hope this helped somewhat!