The above image is good: expression and composition are solid. But the exposure is still off. Now I now you may be going for something dark and moody (and if you are lose the toothy smile) but you are going to hard time of it without some kind of light modifier. I dont think you described your set-up, but based on the image Id say you are pretty much using a bare flash. Shoot that same flash through a $15 white umbrella and marvel at the improvement in light quality. Since you are shooting through the umbrella you can get the apparent light source (the umbrella, not the flash) close to the subject but keep it out of the frame. The science behind this is that light gets weaker at the square of the distance. By moving your light source close to the subject you can expose for the face, or even part of the face, but have a very fast, even and controlled fall-off as the rest of your subject get significantly farther away from the light source.
One word of caution is that you must carefully meter so that the brightest part of the image is not blown out, especially when its a subjects face. And this technique works less well with bare flash. If you dont have an umbrella then move the subject close to a wall and bounce the flash into that. If you have a zoom you can control the size of the apparent light source (the wall, in this case) by altering the zoom setting. Play around with exposure and the distance from subject to the apparent light source.
I still owe you some pictures from my home PC
EDIT:
Here are the pics I referenced in my previous post:
This image was done using a 20"x20" softbox that I modified to be used with a flash and mount to a standard stud versus a monobloc flash head. I think this most closely resembles the look you were trying to achieve. While the image is certainly dark and moody, there are parts of the image that are properly exposed. I hope that comes through on your monitor. The fast light fall-off comes from the fact that the softbox is pointing straight down and is just in front and above my head.
Another single light image here with the same softbox. This time the light is positioned in front and angled at about 45 degrees towards me. I adjusted my distance from the background to adjust the amount of light hitting it. The fall-off I speak about above is evident in that wall (although there is some vignetting added in Lightroom). As you move further from the source the light quickly dims.
Final image is even further in front and above again at about 45 degrees to the subject. Exposure is also higher in this image. I used a second flash on a stand behind me to fill in the wall and fill in the subject. I aimed the flash head straight up but used a bounce card to reflect some light toward the wall. This means most of the light hits the ceiling and fills in much of the scene. This light off the ceiling is similar to ambient in that it will not be bright compared to the key light. But t provides a higher "floor" for your set-up resulting in a more even overall lighting scheme. Don't know what's up with that look...
