For a start, remember that the forest is cut down about half a mile away from the wall (a no-man's-land). That opens for a few neat tri-split possibilities, with the wall where you drew it, a middle third of mostly whiteness (perhaps a few snow-covered stumps or logs or dirt tracks or what have you), and one third of dark, looming forest. Jon in his black cloak would be in the foreground of the no-man's-land, while the wolf should only cover the wall, or it would blend into the no-man's-land too much.
I'm no drawing expert by any means, but I think contrasts would come greatly into play here. The cloaks of the Night's Watch are repeatedly said to be black, the wolf is white, the wall grey and the forest dark. Don't be afraid to go overboard with contrasts, those can be dimmed later if need be. Can't wait to see the finished result!