Focused practice is always the most effective practice! Having a clear goal such as "accurately capture the proportions of the limbs in relation to one another" is a great step to focusing up.
I do see a few issues with proportion - the jumping/kneeling person in the middle appears to have very short calves and small feet in comparison to the other parts of his body, but other figures show clear attention in this area.
Some good and some bad is a good sign that you're working in an area with attainable improvements, so that's about right for right now.
For this exercise, consider working in stages. Do an initial pass, then get up, walk away for a minute, and come back to the same pose. Do a second pass of the same length where you correct your previously captured proportions, either by erasing and re-drawing or drawing over top in a different color. Measuring different parts of the body against one another will be your friend here. How long is the hand compared to the foot in actuality? How long is the hand compared to the foot in your drawing? And so forth and so on.
Hope this helps! Great work :)
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