Tbh for me, you just lack details and need to practice as well.
Btw, this is just my way of doing it. After looking at references photos, I would used 3d model to make it easier for me to sketch. From what I see from your art, you're not adding much of shadows and that doesn't have a light source.
Your reference have a light source. It helps you to place your shadow to make it more realistic (?)
It's better to add texture to your art. Me personally I like adding noise effect (depends on what mood my art is). And as for shades, you can look on Google which shades go on which skin colour. It does help me a lot actually.
This is an example of my art with just base colour Vs details that I add after the base. I actually used 3d model in csp.
- I changed the colour line (so it will compliment the pinkish vibe)
- add shadow
- add subtle light source on the bg
- just add details that I think will suit my art
