not sure if it will help but you can up load someones art with a skin tone you like zoom in and see what colors are being used as a guide .... and i like this drawing you did btw (:

Hiya!
You could try to add some blues into your tones for a more depth into darker tones/shadows. I find that orange, blues and reds help keep with various of tones. I think that orange gives some nice lighting, red helps with the rosy and flesh tones, and blue helps add more depth to your shadows. You could also lower the opacity of your pen and lay red, blue or orange onto your skin tone directly and find which looks better to you!
Another tip I would say is to try experimenting with hard and soft shadows. hope this makes sense ^^; keep going!

@Malkav thank you so much!

@-blake- thank you as well that really helps out!