So I did this private project of Dua Lipa where I tried to simplify and stylize shapes without losing credibility in volumes. I will try to explain my process...

So I always start with a composition sketch. The first one as You see is just a basic structure with the flow of the line of action. From there I go layer by layer redrawing everytime with a little more detail and correcting errors I surely find. At the end I draw the final line art.

Then on below layers I add the basic flat tones...

Next, I add on separate layers shadows (multiply layer mode) and lights (overlay layer mode), until i reach a 3D sensation that I'm comfortable with.

Following, I merge all layers into one and in this case erase line art and cleaning shapes. Also, i may correct some tones or volumes that may not work anymore.

Then, with COLOR layer mode I add base colors. Next, i add color shifts, gradients, color adjustments, and if needed, ambient or secondary lights.

Finally, in this case just minor corrections such as the hand size (which was too big) and eyebrows detail. Hope you like!