A concept "workout". Not thought through very well but I managed to do it step by step instead of running around the process pipeline like a headless chicken.

Well, without the reference it's kind of hard to critique, so I'm only going to talk about edges. The biggest thing I noticed is that you have hard edges everywhere. The problem with that is it draws the eye and makes everything look hard and kills form. Form rendering is soft until it hits a corner, then it can sharpen. If everything is hard, then nothing looks like flesh, instead it looks like rocks. I did a quick paint over to show you some of the things I noticed. Again, without reference, I had to guess at some of these things but I hope it helps :)

Howdy midway I think you could work on construction some more. The rocky archway you made is a nice example of how to do it, it's pretty easy to read, but the rocks on the left of it are a bit confusing to understand. Basically the archway reads like a 3D object (on a 2D space of the canvas) but the rocks read more like a flat 2D pattern. As exercise I would recommend drawing very simple objects from photos and try to construct them as 3D objects and then draw them from different angles. This topic with perspective and construction is pretty confusing so don't worry if you don't get it right away. There's also value but Steve already covered that :D From my experience I could add that trying to do everything at once tends to be overwhelming, so try to decide on what's your intent with the piece you're making. If you're just constructing something, the focus on lineart alone is fine, if it's value then the lack of detail is fine etc. etc. Good luck and perseverance ;D

Day 22 workout Portrait and process study. Original photo by James M. Barrett https://www.flickr.com/photos/jamesmbarrett/6617068397/

Day 21 workout Anatomy analysis

Day 20 workout Portraits, warmups, composition. Attempt at color.

Day 19 workout Composition from abstract shapes

Day 8 concept art

Day 6 & 7 concept art