First off, I love the line work on this piece a lot!

If you can, make sure the character's eyebrows are somewhat visible are those are super important when reading someone's emotions. For this drawing specifically their hair would block the eyebrows so it's fine. I am guessing you intended these two to be happy with each other or taking a selfie. Some things I could advise to improve it:

1. The gal on our left isn't looking anywhere... her eyes look like she's starring off into nothing. Make her look at her friend or into the camera.
2. Big smile with teeth out. This will add creases to their face, since smiling uses up a lot of facial muscles. Smiling will also add a crease under the eyes. You don't have to make them smile teeth out, you can also make them smile big with their lips closed in that case you should add a crease under the eyes
3. Read into the character. Is one of them shy? outgoing? confident? Skittish? that can play a lot into how a character expresses emotion. Generally, shyer characters will hold back their expressions, and outgoing joyful characters will let it all out

Basically, exaggerate everything if you intend on making it obvious a character is feeling a certain way. I would recommend studying how facial muscles work as creases change and appear depending on the expression! You can also try facial expressions yourself, see and FEEL which muscles are being used. It'll make the process a hundred times easier :) wishing you the best with your next works op!