Rate my work, /ic/ What can I do to improve my skills?

Work on your perspective

don't smudge so much

>>2852559
That paper blending nub is not your friend--they really prevent your values from getting a nice contrast. Use and eraser to clean things up, and use fine lines to hatch and cross-hatch to shade instead of scribbling to get something dark in the spot to buff out.
Study a reference and actually use tools like perspective to figure out how objects sit in a three dimensional plane.
For organic objects, break them down into three dimensional shapes to be able to accurately recreate them, much like a 3-D modeler might.