I want to talk for a moment about facial expressions. I've been noticing them quite often in the manuscripts I've been editing (including my own). I've also been hacking away at them with my red pen as if they were zombies and this were the apocalypse.
We writers are obsessed with facial movements. You can tell, because we include so many in our manuscripts. Our characters smile and frown in a variety of ways, from small quirks of a frown to wide, brilliant smiles that stretch the lips. Characters lift their eyebrows... in surprise, in question, or in amusement. Oh, they also waggle them. Eyes widen and blink, or narrow or roll. Lips twist and purse. Mouths snap shut or drop open.
And I haven't even gotten to the head-movements, like shaking or nodding or tilting. In my own writing, I'm fond of having my characters tilt their heads, so much so that they probably require a chiropractor by this point.
In many cases, if a reader didn't know better, they'd think that the most important facet of fiction is what a pair of eyes are doing at any given moment. Gazes sweep and penetrate. Sometimes, glances are meaningful or full of weight. At other times, stares can burn through a character like the Death Star through an entire planet. And you think Alderaan had it bad... woe to a character when the heroine's eyes are boring through him with fiery anger!
Now, description in writing is a good and wonderful thing. So is the ever-expounded upon concept of showing. So, it stands to reason that we need to describe the reactions of our characters. But there's such a thing as overkill. Facial movements are probably one of the most overused and cliched method of providing beats in a scene.
Facial expressions can be very useful and important--we see that in real life when we talk to other people. However when they're overused in fiction, the one moment when it's important that the reader see the tiny frown of the heroine, they're not going to notice in the sea of other facial ticks. It's just another frown. Just another glance.
We also have a strong compulsion to describe the facial expressions of point of view characters. One small problem with that--the point-of-view character can't see her face. And while we can be cognizant of our own facial expressions--we're often not.
When I'm furious, I'm not actually aware of anything my face is doing. I feel like I want to throw something. I'm aware that I can't seem to breathe well and that there's an odd ringing in my ears. I see that my hands are shaking. But do I notice that I'm frowning? No. Heck, I have no idea what my face looks like. Neither, for the most part, should a POV character.
So save those facial expressions for moments when there's an important reason for the POV character to be aware that they're smiling or frowning. If you've conveyed that the POV character is happy through narrative and dialogue, the reader's going to paint a smile on his face. Readers are clever like that. And it's what makes books different from movies--we can suggest how the stage looks with hints and bits of description. The reader fills in the blank bits when we give them enough to build with. The facial expressions of characters are no different.
And honestly, if you need a beat of some kind, there's a million other things a character can do besides smile or glance.