Hey ga3. Ditto everything Melissa said. Just keep building this drawing, I realize that it is a work in progress. If I may point out a couple of things. Keep track of your light source, it's on the left side of the photo, right now the drawing is lacking shape The right or shadow side of the drawing needs to be built up with with some pencil. Build it up slowly until you like the depth, the same with under his chn and chest. Balance is key!!
Becareful of hard lines, I know the shirt is untouched, those hard edges have to be blended out to create the edge, this will give it a natural look. Lastly, the drop shadow under his arm is really harsh, I usually start my shadows half the final size and keep pulling them out with a tissue or Chamious, this will give you that nice soft vignette your looking for.
Hope this is not to much. It's a really nice shot, your friend will love the final piece.
Peace!
Marc Forest.
http://www.marcforest.com