First need to address where your light source is
#How Can I Shade Like This?
tame reef
viscid inlet
hello miso, the collar bone would have a slight shadow under it if it protrudes out
brazen crane
start by studying their work i guess
tame reef
A slight anatomy issue I noticed, in female bodies, the arm is behind the breast.
For the shading, their shadows are more Saturated, just use the skin color make it more saturated then darker. Rn yours doesn't look saturated enough so it looks full and muddy
modest stump
Thier colors are much more desaturated, you would have to make the skintone more desaturated, they have a very good sense of the the shadows should go and where the focal point in the drawing is and that focal point is the expression and or just the face. And the hair makes up their shading alot so you having a fully no shaded hair makes it look like a different artstyle? Coloring style? Idk. I would recommend on improving on your facial features like look up how to draw facial features individually, and how to draw them in any perspective.
shadow cove
If you want to learn to shade in a certain style, I would recommend trying to create exact copies of art drawn in that style as a form of studying. The people above have already given pretty good tips!