Samurai (Quick Sketch)

Usually, when I'm really stuck at finding idea on what to draw, the thing I do is quick sketch. The time limit is mostly 1 hour with more or less of it. I realize that I'm still low at value knowledge, so I'd like to improve more, with this quick sketches. My problem is actually I'm still hesitating in putting high and low contrast in creating value, as well as little bit of rendering issue (which I'm constantly practicing to be better).
So, for this time, a quick sketch of a samurai.

Ref: None
Total time: +- 1 hour