I really like the compostion so far... For the hair: you should see the hair as compact forms and not draw every single hair itself >https://www.youtube.com/watch?v=VDIuwfkRoeo< marc has a tutorial for it, I don´t know if you check this one ... For the lighting: you got more a ambient light; try to define from where your main light is coming (you can even draw a arrow, sun, ball .... as guide, not included in the finished piece)... and maybe give your characters a rim light also.... Good luck
