I'm new to SVS and I've just started with the "How to Draw Everything" class by Jake Parker in an attempt to finally learn drawing/painting/illustration in a deliberate, more formal manner.
The first exercise is upside down drawing, which I've done before.
Here's the first time I tried it a couple of years ago...
A couple of years (and not really much drawing in the meantime later), and here's my upside down version of Skullchaser (I don't think I have to tell you mine is on the left):
I'm happier than I expected to be with it. I don't have the line confidence yet, but I did much better with my proportions than the first time I attempted this exercise.