Help on trying to achieve a specific type of shading
It looks like a style in-between line drawing illustrations and (a lighter version of) a typical comic book inking style.
It is a high-contrast style. Only deep shadows are filled in, so the rest can still be coloured in (by another artist). In this case, though, it is likely used as a stand-alone style.
Characteristics:

Deep shadows are exaggerated, and drawn as flat areas.
Shadows are added sparingly and economically.
Reflective surfaces like hair and metal often have additional shaded areas to emphasize their glossiness.
The darkness and/or pattern of a material is sometimes lightly indicated by additional hatching, like the pants of the person on the left and the scarf of the person on the right.
A subtle use of line weight (e.g. the contours of the clothing).

Try seeing your model as if lit from above by a very bright light source, like the sun, and find out what areas will be completely covered in shadow, like folds in clothing, and areas obscured by cast shadows, and only ink those areas.