The relationship between facial expressions and muscles is clear: expressions are created by the movement of facial muscles. Manga characters may be deformed, but you can improve your drawing ability by understanding how their muscles move depending on their emotions: anger, sadness, and pleasure.
There are four basic facial expressions:
Incorporate the four basic human emotions—joy, anger, sadness, and enjoyment—into facial expressions.
1. When I'm happy, I look up at you.
I want to see the expression on your face when you're happy. The eyes, eyebrows, corners of the mouth, and other parts generally face upward.
2. An angry look is characterized by lifted corners of the eyes and eyebrows, with sharp lines becoming more common.
A sad look is defined by a downward vector, with the eyebrows and corners of the mouth sagging.