Aesthetics Please help

To begin with, that faceup looks very good to me If you'd want to give the eyebrows more dimension, there is the technique of putting a pastel shading base layer (but I guess you'd have to redo the entire faceup for that). I also think that using darker colours to paint the hairs in addition to the white and grey, would make them seem more real.
A good rule of thumb to keep in mind for this (and painting in general) is that you're not painting with the colours the objects actually are in themselves, but with the colours as we see them --in this case that means you have to use darker colours to give the illusion of shadows, because it's a flat surface and there won't be real shadows.

(For inserting pictures, the FAQ has a helpful guide )

 

Acrylic is a useful tool, but needs some time to get used to. For something like white on tan it's pretty much the best choice because white pencil just won't show up as well.

However, some things you should try:
- blush the eyebrows shape first with pastels
Take a little darker shade, like a warm gray, to do so. Afterwards seal the head and then paint on the details in white on top. Do so in two rounds. First time lay down all the hairs, seal, second round emphasize several hairs by painting over them again. That way they don't look all the same and you get a more layered look.
(old example, but you can see the blushed base here:
https://i.ibb.co/dgX7gmJ/IMG-1602-Edit.jpg )

- dilute your paint
Absolutely needed! Otherwise the paint is too thick, hard to handle, dries crusty and so on.

- shading can be more bold without looking weird
Be a little more brave! Just make sure not to heavily overdo it with bright, saturated colors. Instead try to softly layer them and imagine it like a scale from light to dark. For example, you want high cheek bones? First lay down a basic blushing layer that is a bit darker than his skintone, afterwards add another darker hue of this color to the bottom of his cheekbones. You can also try using a gray shade to add shadows to a face. I usually do that softly to nostril folds, the inside of the ear and so on. Just like shading a drawing.

- take your time
You have all time in the world to paint a head, and you don't have to do it all at once. I usually allow myself several days to finish the blushing alone, then a day for the basic acrylic parts, then another day for enhancing, another day for finishing. Only thing I recommend is to always do both sides at once, i.e. when painting eyebrows finish both of them and don't just do one side and then a couple days later the other. Just harder to match them then.

 

Well, I want to say that this face up it stunning! Excellent color choices.

I'd say that the pastels for eyebrows works really well. If youre careful and use a light greatly you could probably add pastel over the existing eyebrows then just re add the white where nessisary.

Shading is also really important. Remembering that the eyelashes are actually 3-D objects not just lines under the eye. I like to imagine them as tiny little curve shapes under the eye and draw then with a slight curve rather than just a straight take. It doesnt have to be extreme at all, a slight curve makes a huge difference.

 

Your hand is very steady. I commend you.

I have little experience with faceups, but I've been doing artistic things for years. Self-doubt can be incapacitating. Stepping away, taking a break and looking at a project with fresh eyes can be a big relief.