I learned to do shadow first in highschool when I was doing fine arts (in fact, lines and perspective were never focused on despite how important I think they are now), while in animation classes I was taught to do line and discouraged from shading.

First drawing is before animation classes, second after... I guess it's why I discourage shading until you got your line, skeleton...foundation crap sorted out first :/

Actually I like the left one better (Even though I think both of their anatomies could use work). Drawing anatomy from the details out (Starting with individual muscles) is fine, if one has a good idea of where everything will end up.