If you don't mind:
The thing is, I think what you need to worry more about is the shape of your hand, rather than lighting or rendering. As of now, it is hard to make out if it's a hand or something else. Clarity first. Considering that this is a book cover, you'll have to think about how it would look zoomed out as well. Make the hand larger. Also, what I learned about composition is that horizontal placement equals calmness, and it doesn't spark interest. Make it diagonal, swirl, or whatever.
This is a rough sketch I just did, if it helps:
One last thing, a general tip when drawing is to use long and confident strokes to avoid wobbling lines.