Head value study

So this is the semi finished value study, as in there's still bits I could neaten up and tweak but I cant be bothered . I'm pretty pleased with it overall anyway, it was a good practice and I think I'll do a few more because learned quite a bit in the process of painting it. I'm leaving the reference photo in the wip upload as If I stick it right next to him all you're gonna see is whats wrong with it rather than appreciating it in its own right .

Also if anyone knows I'd like to know how to push this further to make it more realistic, I know if I used a soft brush I could blend the skin better but apart from that what would make it more realistic, more value and different tones? I'm not really sure how to go about taking it to the next level.

Reference/wip: [link]