In the order that your latest sketches are posted, it looks to me like you are taking steps in the right direction. The bottom page looks a bit looser and I can spot some areas where the line weight difference is starting to add that "sketchy" POP that we all love so much.
You might like to try drawing cubes to warm up and then filling in the sides with ellipses like in the example below (actually just found the site but it has a lot of good info if you keep looking, is it from another C77 poster?). I noticed after doing only pages of ellipses that it was harder to draw an ellipse in the context of the rest of a sketch, but this helps that.
Thanks for the post Robby-Roy, good stuff! I remember doing that exercise in first year but I was never really good at it so I think I gave up. Gotta get back on the horse! Some more exercises I've been doing:
I like to weight the lines heaviest at the bottom and sides. Try more cross contour lines to show form. Get into the habit of putting down a quick axis before you draw any ellipse that needs to be oriented to something else.
remember, if your tool doesn't allow line weight variation with pressure changes, like a pencil, you're going to have to lay down multiple passes to get a heavier line.