You kinda listed almost every fundamental haha, but I feel that struggle. I think that the best course of action for your study is to focus on one thing at a time. So something like perspective or anatomy. Of course you can draw whatever you'd like, but I would mix in study of one fundamental for a week or two at a time rather than trying to master everything. Light and color should come last as they are informed by your draftsmanship. Getting a clear drawing with strong structure and anatomy and gesture would help the lighting come through later. Your drawing was a bit unclear of what the characters were doing so I tried out the pose with clearer lines and line weight. Really focusing on what is in front of what and keeping the proportions and anatomy in check. | Artwod Feedback