a friend asked me how i manage to put so much physical volume in my sketches and the short answer is The Bean
in brief: 3D shapes in space don't just join, they overlap where the surface becomes perpendicular to the viewer. and where they overlap is where you want to draw a line to accentuate that. The Bean is both a good visual reminder of that and an exercise in quickly creating solid 3D shapes and getting your hand used to that -- i'm still practicing that but it's giving good results so far
it's the difference between these two pictures:
same exact starting sketch with a single line added to the one on the right
(the long answer is a lot more complicated but this is a good starting point if you're learning to draw)
only drawing lines for a character's outline is a mistake that a lot of new artists tend to do -- and one of the many reasons why tracing isn't going to help you understand how art works. you have to first think three-dimensionally and then represent those forms in space, which takes time and a lot of exercise
(big thanks to @saucy whose sketch of a bean gave me an extremely straighforward way of both conceptualizing something i was already practicing and to explain it to people)
