Like the flow of the overall pose, and you have lovely lively marks. I found the crossed arms a little difficult to read, which might be helped by stronger shadows. But really nice drawing.
It's important to use construction lines before you go into the details and you did a great job with this I specifically like your shading. Something I would suggest (especially when it comes to quick figure drawing) is to not rely on them. Try to add a kind of organic fluidity into your fast sketches by using long strokes and solid lines rather than the, most of the time messy, short stroked etching with your pencil. It will help your sketches become less stiff and unnatural.
Hope this helped!