several people have asked before how i draw expressions and i never really know what to say except to just study the faces other people make. look up references on expressions like shock, anger, surprise, etc. or, as i usually do, take photos yourself and use those as reference images. sometimes a mirror is a surprisingly good reference helper.
one thing i try to keep note of are the wrinkles on the bridge of the nose. whenever someone is snarling or making a disgusted face, there are going to be tons of wrinkles around the top of the nose, and at the corners of the eyes. but the problem is that even an angry face can look different without the wrinkles. adding in those few lines, regardless of the expression, can make a world of a difference with the look the person is giving, so keep those in mind.
(also sorry for the bad photos it’s 4 am haha)