When I was illustrating The Adventures of Cedric the Bear I did lots of drawings showing different facial expressions.
This is a great drawing exercise. The easiest way to do it is to draw a series of simple faces, like a cat’s face.Then choose five different expressions to draw on the faces. They could be: ‘Happy’ ‘Sad’ ‘Grumpy’ ‘Worried’ ‘Laughing’. Sometimes I make faces at myself in the mirror to get the right expression! Or you could ask someone else to make the face and then see what happens to their eyes and their mouth and very importantly to their eyebrows….