Hello! I find, when using a real life model of someone in that similar pose (you will find tons especially in HP Cosplay), it makes the drawing process much easier.
I also used "Anatomy drawn Easy" by Christopher Hart. Invaluable book. Its tricks are so simple that within a month you will know how to draw a human from top to bottom without a fuss! As for the shading, same, real life examples help give you an idea of how to shade. I usually set one corner in the drawing from where the light source comes. As you can see in your drawing, the shadow of Hermione on the wall actually contradict that of her body. That could be one reason why you felt that the drawing looks a bit off.
. Hope my critique will help you in some little way!