>>149269735An exaggerated expression exists to punch up a joke, not create a joke. "Ed eats his whole mattress" is a joke, how you draw it really sells the execution. You should be able to look at an expression isolated from its context and still have a rough idea of what the expression is conveying other than "silly". All expressions are created equal. There is just as much effort put into a sad Ed face as there is a happy, screaming, angry, and confused expression.
Solid cartoon construction helps. When you actually keep in mind the character's form and skull and try to exaggerate it around that rather than just drawing anything and slapping a face on it, it feels like the character making the face rather than just "a face".
It's hard to put it into a science, because humor doesn't work like that. But you can tell when something is and is not funny, when someone is trying too hard and when they're naturally funny, and you can tell when something is trying to be a reaction meme vs. just a really good expression.