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Oh, wow, the lady on the right is a remarkable jump forward in skill level. The lines are cleaned up, and the shading shows a good understanding of human anatomy, even propely indicating joints, muscles and fat tissue under the skin.

You are misundertanding the process actualy. First you need a better grasp in volume and the space occupied by these volumes, then you go for basic structure to solid structure and only then go for anatomy. But, it do work to learn a bit of anotomy first, then go back to volume, see a bit more of anatomy, go back for structure, it is not a linear knowlodge, saying this, go to Proko anatomy free course, it will give everything you want to know,

Cheers, and to better define the shapes and do a proper render, see the lighting lesson, at least the first one, where he explains the light theory of core shadows, halftones and etc