These value studies are great! I like the different compositions you explored and your shading is nice and clean. I think you could make these even better if you separated shapes with value contrast rather than lines. For example on the 2nd one, you could separate the shirt from the skin by making the skin a darker value than the shirt. And rather than drawing individual lines to represent the folds, you could add a group of small shapes of value that fan out of the knot. This way you can connect your shapes with a sort of rhythm. Hope this helps!