Hi I am not an expert myself, but maybe I could help you.. even if just a little bit.
On your first page, I really like what you did on the left, I feel like you captured the motion well. The one on the right though looks like you spent more time on it, but the result is not as good to me. I don't know if your model really looked like that, but the booty area feels wrong. And the top of the back, maybe because the lines are a bit messier. And most importantly, the figure on the right feels plain compared to the left one, and that in spite of the shading you added. I think maybe you should try practicing "the bean", it could help you get the right torso/hips relationship, especially for bent figures.
Regarding your other figures, I really like the 2nd one, even if incomplete. It started alright to me. And for the rest, I am a bit inconfortable with the hands, it gives me a bit of a scarecrow feeling. But it's not super important, don't change it if that's the way you prefer to draw them ^^
I guess that's all I am able to say. Thanks for sharing your sketches too and keep practicing !