Back in the day guys sure knew how to relax. Look at Clark here, pipe in his teeth while doing some serious tinkering on a car engine. (I didn’t make it up, I found a photo reference of it.)
As a warm up I’m just looking for one or two successful elements in a sketch. For example, I think the lighting on Clark’s arm closest to the viewer was a success. Other than that the sketch is okay. It mostly consists of me testing out different brushes in Manga Studio 5.
The biggest thing I don’t like about the sketch is that when it’s slightly minimized the brush strokes look too airbrushy. At least more so than I like. But that’s the thing about sketches–learn what works and what doesn’t.