I love how you catch the light and shadow on most of your figures. Your self-critique of your short sketchy lines is something I struggle with myself. But I do see some nice long lines here and there, so good job working on that!
You seemed to portray the overall figures very well. I suggest perhaps considering why you didn't get to the shading in some figures in the same time frame while you did in others.
Muscle control is a pain, I find myself researching warm-up exercises constantly. Try looking for new ones. If some don't work, don't keep them though, different artists seem to find different exercises helpful. I do dots and then try to connect them with perfectly straight lines in a single stroke.
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