I used to go to school for art so I could be at least a little bit of help.
What I normally do is figure out where the source of light is coming from. From what I see with yours, is that it is coming from the middle of the piece, reflecting off of the character, which leads to my next point:
How will it reflect off of the character?
I have noticed that since the light is coming off of the edges of the character (since the light source is behind the character) I would then go from there.
With the shadows on this one, it makes sense. However, if it was a bit more darker around the middle of the chara (nose, middle of the coat, etc.) then it would be more realistic.
I have some examples here:
I hope this helps at all!!!
Adding onto this, this can work with objects or basically anything around the setting as well (ie a ball, grass, different objects).