Can I make a suggestion?
I notice that there is a distinct jump of skill from your drawings to your 3d renderings... I think that if you close that gap in skill you will improve exponentially.
I suggest that you take some 3d shapes, circles, squares, peanut shapes, doughnut shapes... and try drawing them in pencil (or digitally if that is easier) and try to get it to look EXACTLY like what it looks like in 3d. Get the clean edges, the smooth (or hard) transition of shadow to light, the cast shadow and the shape all correct. Work as long as you can on it until it is as perfect as you can make it... then try more complex shapes like that dog, or the fat cheeks, or your car model.
"A papercut is a tree's last revenge."
dA | Sketch | alt dA