I think what's great about your drawings is that you have good proportions, but what I would suggest is to work more on your fluidity of your lines, and try not to pay much attention (within these drawings) to contour as much as gesture. Try not to sketch your lines with small strokes, but rather with one fluid motion. "Ghost" draw the form first to loosen your wrist and shoulder, and then in a few lines, lay out the action of the pose using "CSI" meaning... all of your lines should resemble these three letters.
If you ever get the chance, I recommend looking up Proko (Stan Prokopenko) on YouTube, or go to Proko.com. This guy has an amazing understanding of form and gesture, and has really good tutorials through YouTube.
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