Thanks a los for the advice! It's nice to see how great pixel artists like you try to help the new ones 

This is one of my first works and I tried to inspire it on a photo, so I was a little bit lost hahaha

I hope my skills will improve soon!

You have quite a lot of pillow shading going on, plus the lineart itself is fairly jagged. You also don't need strong outline to define facial features, a quick (not perfect) example of how you would accomplish definition with shading: i.imgur.com/ycXfRAM.gif

Of course, the outlines might be a stylistic choice too, but even then they're a bit jaggy like the rest of the lineart, and the shading for example on the nose and hair don't quite work.

The purpose of the background is also a bit lost on me. But still, a good start.