something off the bat I'm noticing about your referenced studies, is instead of focusing on drawing what you're seeing, you're drawing iconographic representations of what you think should be there. get away from going over the same line more than once. If you didn't draw it right the first time, erase and redraw it, no matter how dark it gets, it won't be more correct-- that sounds silly, but it's soooo true.
also, with your reffed figure studies. throw your reference image into greyscale, and work on getting those tonal values down. it'll help you get away from those hard dark lines you are so dependent on. Lines are just visual representation of large abrupt value shifts. Just look at DanielC's stuff...his pencils are a perfect example.
If you can, set up a simple still life with a single light source, and spend a couple hours on it, trying to get everything as exact as possible...you'll learn a ton about observation.
most importantly, draw what makes you happy--switch up your studies with drawing from imagination. Try and figure out what you've learned from your studies and apply it to working out of your head.
keep working hard, it always pays off~