One of the interesting things about learning how to draw cartoons are the faces. Especially how a small difference in the angle or thickness of a line can make a huge difference in the expression of the face.
Try it. Just draw a circle as the face then add different eyes, nose, mouth and eyebrows. Come up with a few versions and then just change the eyebrows. It is strange how a small change to the tilt of even one eyebrow can give a very different emotion to the same face.
Do you think about facial expression when you write? Do you give your characters a face or just tell people they look annoyed? How do they look annoyed, how does it show in their face. Show, don’t tell.