Obviously there will always be "fallback expressions" that get used over and over, but I'm always surprised by people who like... pre-draw a head in a basic neutral expression and then copy-paste it for drawing pages because I'm always like "...but how do they get the nuance of the expression?"
The human face is very expressive. It has a lot of different moving parts to it. So when drawing expressions, I always want to try to get across as much of that as possible, and for comedic purposes, I also mix in simplification and manga or cartoon shorthand.
It's important to think about what exact feeling your character is experiencing right now in detail. Just "happy" or "sad" aren't enough. You need to really get on in there.
When people are excited or afraid, their eyes tend to widen. It's a reaction to make our eyes take in more light and see more and react more quickly.
ie. "Rekki is excited about the prospect of violence". Her eyes are wide because she's excited, and her eyebrows are pulled down adding a fierceness to her wide grin.
"Felix is desperate and harried." He's been given a really important short-notice order he's not sure he can fulfil. His eyes are wide, but you see the eyebrows pull up into a mixture of fear and confusion. His mouth is a grimace like a caged animal, and even his neck is tensed, along with his shoulders.
When we're angry, fierce or confrontational, our eyebrows tend to go down, and when we're leaning more on the "flight" end of "fight or flight" and we're scared or want help or to avoid a conflict, the eyebrows tend to go up. Raised eyebrows can also communicate a sort of "lol, okay I won't fight you but I'm skeptical" kind of tone.
Just as eyes can widen to take in more information, eyes tend to narrow when we want to see less of a thing because it disgusts or confuses us. That said, the eyes can narrow in different ways for different reasons. The eyes being pushed up at the bottom into a more arched shape is a characteristic of smiling, while the upper lid drooping over can show tiredness, boredom or disdain, but can also show relaxation and therefore confidence.
"Rekki is incredulous" It's like mild anger, but pulling up the lower lids to narrow the eyes creates and expression of "WTF ARE YOU TALKING ABOUT!?"
"Urien is confident and also being an absolute creeper and flirting with a fourteen year old girl to manipulate her, seriously what the hell, Urien?" The upper eyelid is relaxed and low here creating what's called "bedroom eyes". Bonus background Sarin here with an expression that's a mixture of incredulity that he'd even do this and disgust and anger that he's seriously doing this.
Basically I never feel like I have to avoid drawing the same expression over and over because I always try to draw an expression that's very specific to what the character is feeling, and that's almost never constantly the same for more than a few panels if the scene is dynamic and actually changing the status of the characters (and if a scene isn't changing anything... why is it even in the story?).
