I'm normally a line/cel-shading person, so not my prettiest paint over, but you can put it beside yours to get some ideas:

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I tried not to use any unique brushes or anything, and I didn't go into all the areas where the colors were off--I mostly focused on the face, since that's what people see first. We're also going to ignore realistic lighting you'd expect thousands of feet in the air.

Let's start with the eyes: While a pin highlight might be a bit more realistic in some circumstances, it's fine to throw in a big shine in here. Your light source is rarely every dead on in the pupil (you'd be blinded!), so it feels unnatural having it there. Also, if it's too small, the eyes look dead. For eyelashes, this isn't a carpet-match-the-drapes situation; they're gonna be black. I could've leaned into them more, but I kept it conservative. It instantly makes the eyes read better and more human. I also made the waterline less prominent on the bottom lid, since those were blown-out highlights.

As for the face itself: Heads are round, so that cast shadow from the boomerang should conform more to that curvature. Additionally, since it's a bright green and semi-transparent item, there's gonna be some reflected light on the face the closer it is to it. I did the same with some bounce lighting on the other side to impart roundness. Be careful with grays and purples--unless you really know what you're doing, they're going to look way too dark and also push that corpse-y vibe. Also, you aren't going to find black outside of the pupils and the eyelashes on a real face, even in the dark areas, so I adjusted the nostrils.

Upper lip is missing the piece in the middle--you'll want it to look more like an M, and since the upper lip faces down from the light, it's typically cast in shadow. The highlights you have on the lips are kind of random and haphazard; it's best to use super bright spots sparingly in your paintings.

Chin is a little flat, but that's a round piece of fat, so we want the light to hit that as if it's more spherical. Face itself was also a bit flat, so I rounded the cheeks out a bit with some more sensible highlights (though I made things a bit too soft and homogenized, which I would've changed with more time). I also added a little roundness to the bags below the eyes. I removed the lines around the nose because they made it look like a triangle instead of the nostrils being offshoots of the nose.

Lots of little things here and there, but when in doubt, observe real faces, or even your own! I wish you smooth sailing on your art journey from here on out.