The shading on the second and third piece are much better than the first. I would say watch out for outlining the body in hard lines, they tend to flatten a figure. You do a good job with soft line variation in the first drawing on the shoulder farthest away from the viewer. Keep up the good work.
Some crit for the figural work: keep studying anatomy and folds as already stated before me. Study your proportions carefully and remember to work with the largest shapes of the body, the cage, the head and the pelvis, first and foremost. After that, you can move in to more detailed line work.
When shading, attempt to be a little more "painterly" about the values you put in. By this I mean once you have a gesture in place, lay in the largest areas of value and move into some further detail from there.
On the folds and the portrait in pastels, make sure not to leave the white of the paper showing under the color, in this case, it ruins any attempt at form or realism you have worked for.
And on the machine, work on your perspective drawing. As with all your drawings, try to work loosely at first and refine your lines and detail once you have established a gesture.