This is my first critique, so please bear with me:
1 - How long did you spend on these? Depending on the times ( ex. 60 seconds or 5 minutes ) I would like to make specific recommendations to help you improve overall in gesture/form. For example, drawing in shorter periods of time could help you better understand the basic form of the model. I'm not saying to rush or anything, but something like working with less time forces you to draw the basic actions described in the model, which will help when drawing without and with a reference. (Note: Drawing without a reference is just as important as a study!)
On the other side, if you were drawing for an extensive amount of time, you should see if you can notice how the model can be seen as simplistic shapes. An example of this is instead of seeing an arm as an arm, try and imagine it as a retagular prism connecting from the shoulder to the middle of the arm. After that you can build up those shapes to more complex values and forms. You'll be able to notice these more and more with time, although reading an anatomy book and making notes could also help quicken the process. Understand that the process of learning takes time.
2. Drawing with your arm can help improve the fluidity of your drawings and will reduce the choppiness of the lines. Be sure to also start your next line from your previous one, for that will also help the drawing feel more alive.
A good way of practicing this by getting a blank piece of paper, drawing a single vertical line down with a pen, and begin drawing a line from the previous spot to the right or the left 8 times. Be sure to space each line from each other properly. Then, begin to increase the length of the lines until they reach the opposing side of the page. Note that for this to be helpful you have to do this daily. Finally, begin doing the same practice with curves instead of straight lines. You may not see anything improvement in line quality for weeks, maybe months. Remember, patience is key.
3. This is more of a piece of life advice then anything, but I feel that it is important to say concerning art as a whole. Do not compare yourself to others, for if you do you will never feel good enough. Instead, try to compare yourself to yourself. Continue to improve on the issues you have at this moment, and you'll be able to do anything.
I hope this helped. Good luck !!
