I can't ace this picture sorry ... Let me begin with all of thoughts that I had on a first view, than I will examine and tell my opinion about how to make it better.
First at all what hits me is wrong lining-up. Why don't we see all of the action ? His instrument is the action, his body is the action, his dress is the action and even though it is a small peek, the background could be a great action.
What could you do ? While bringing it to a bigger composition and letting us enjoy to examine the details, you could also work this picture in black&white.
If, this is a portrait try, then you should definetly zoom to his face a little bit more because he has a nice way of feeling his music :)
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