Cool! that's a really great looking head someguy. the only thing that stands out to me are the polys on his nose - i might not have them come to a point like that - though on the smooth head it doesn't look too bad.
Personally Id lose the tris on the cheek crease area, Its a would-be deforming area, if you are going to do animation. Also for arguements sake I'd also lose the tris on the nose. But thats just me - no tris!
Not bad but lots of room for improvement. I would get rid of alot of geometry on the face as it very cramped in there. Also have a look at some of the earlier posts in this thread on edge looping the mesh. The post previous to this is a good example by Some Guy, its a nice mesh to work on.
Its all just practice at the end of the day, keep at it
I also have a question - What is the best poly formation around joints (for skinning purposes)? Obviously there's a difference between joints, so can you also post examples for different joints eg shoulder, elbow, wrist, neck etc.
I would try to keep it all quads, no tris, that way you can use the edges to define the loops of the face.
I would watch the placements of the poles, try to have them in areas that dont move when animated, the ones that stand out is on the nose, if the mesh is animated then the placements of them could cause funny problems with the mesh.