Following on from the comments in the last post, I decided to do some more to the drawing. Firstly, I darkened the background to push it back as suggested by Sue. To make sure I kept the boy behind the glass I did as Pat suggested and darkened the edges of the raindrops. I also darkened the lower part of the boys shirt to make it look less even and I've done a little work with the hair.
The changes have significantly increased the contrast of the drawing and given the whole thing much more depth. I don't know if it is something I see because I want to, but I also feel the drawing now has more atmosphere and mood.
Thanks to everyone who commented previously but especially Sue and Pat.