Aesthetics Feedback for 1st Faceup Ever

I will start with a compliment because for a first faceup, you did very well!

Now onto some critique. I'm not sure what size brush you were using, but you may want to get a smaller one. A very thin brush with long bristles can help get those fine lines cleaner. Your gouache paint also seems a bit thick. If you add a couple drops of water, it can thin gouache paint. Play around with how much is needed. Finally, watercolor pencils need to be kept pretty sharpened so the lines stay thin and uniform. So keep a pencil sharpener handy!

 

I think you're off to a great start - the faceup looks cute and not as bad as you think!

I second that getting some thinner brushes and thinning down the paint will help you with neater lines. If you have a hard time getting the lines nice on a 3D object you can practice on an egg's shell, for instance, if you don't want to practice on the head itself. Water and gouache is an option, I've personally found acrylic thinner + gouache or acrylic works better with bolder/sharper lines, though. For thin brushes, you can also look into nail art brushes as they are not very expensive and come in many bristle lengths so you can try out what fits best for you. With anime faceups you don't get the same amount of room for error that realistic faceups have so practising strokes will be very helpful in the long run!

I think you've done a great job picking the colours for your faceup! The lashes will look good with a little bit of brush control practice For the brows, you might want to play around with the shape/length and placement a bit as they currently seem more like an extra eyelid crease. The mouth looks a little dirty/smudgy at the corners - if you made the line with a watercolour pencil, you might want to switch to a brush with some paint there for a neater appearance (it'll also be easier to get into that crease there like that). It's one of the parts of doll heads where you can't really get away with errors that well so figuring out how to do it in one or two smooth lines will help you make the whole package look neater.

I'm sure your next try will be even better, hope you keep us posted with how it goes! You're doing great already, it'll only be uphill from here

 

It looks good for a first faceup actually! You used a bunch of different color ranges and even some blushing, which is pretty nice

Now for the actual critique: For the kind of aesthetic you're seeking, you'll probably need thin brushes. Waaay thinner brushes. Like those nail art brushes that do super thin lines. I think gouache might not be a good choice of paint, because it can get thin super easily, and you don't want "watered" kind of lines. I'd pick acrylics instead.
If I was trying to do this style and didn't get the brushstroke quality I wanted, I'd try "stencils" too (cut out the shape of the eyelash lines you want and airbrush over it). Worth a try... maybe...