/ic/ - Artwork/Critique

I think I'm getting the hang of understanding shapes/gesture and how to apply it in figure drawing, and while I'm far from great I can see some progress in it. The main problem right now is understanding values/rendering, most books I've seen go "okay, here is core shadow, half tones, highlights, cast shadow and reflected light and this is how you apply it on a sphere" and while I managed to do that, I completely fall apart when I try to apply it on a more complex form. Do you guys have any resources or tips on how to get a better grasp at it?

Pic related is my attempt at eyes. First one is from imagination and second is from reference.