drawing boxes and cylinders is just as important to be honest :P
until Legomaestro drew 1000 boxes I hadn't seen anyone draw 1000 of anything either XD
heads from behind dont have much face detail such as eyes/nose/mouth, so I don't draw them for practice very much. also since the silhouette is the same, all I have to draw is a normal front facing head, and trace different lines over it to get a back facing one!
hmmmmm my process huh. Really I just draw on auto pilot, and generally don't draw the exact same thing twice for variation, so I say:
-ok lets draw a face at 3/4 view
-now let's try one with larger eyes
-now let's try one looking downward slightly
-ok bored lets do a front facing head
-lets try a chibi style head
-etc
I often try and mimic art styles that I like, and so I vary between realistic and "manga" styles quite freely :P
edit:
more faces 680/1000
legitimately no idea what I am doing :P
Edit2:
Did some sketches. Did all the poses first then went back and added details for all of them.