uuh, I think it depends a lot about what style do you like? My best advice would be to study the artists you like more, to see how they do expressions, and notice how many details they put in faces… Personally I like a lot to look at disney characters sheets, and some other comic artists I’m following as spiritual teachers.
When I study an expression, I always start with a general, very simple, toony sketch, and then I draw over them, trying to save the original expression…
of course I lose a lot of freshness in the process… indeed, I like the initial sketches more :°D
Then remember that we have 30+ muscles in the face, for expressions and chewing, and they all can be used to combine an infinite variety of expressions. You don’t have to exaggerate the features just to express a different emotion.., some changes can be really subtle, and still you can understand what’s going on!
Also, friendly reminder: eyebrows are your best friends. Love them
So yeah, I hope this can makes some sense!