Bjorn van Sinttruije wrote:
Try shining some light on the background, so it will become lighter and make your subject stand out.
I agree with Bjorn's observation. There isn't enough contrast between the background and your subject. You have several options on how to achieve the contrast, of which a background light is one. Others can include changing the fabric backdrop to a lighter or darker colour (the current one in monochrome looks similar to the skin tone), using a natural light source and reflectors rather than flash, getting the flash off-camera, and playing with the DoF.
Here's what I mean by natural light.
This portrait was taken on a cloudy day with light coming in from the right of the frame through a window. A reflector was placed on the model's lap to lift some shadows, and the tilted composition to flatter by creating the appearance of a longer neck. Further to the lighting and composition, I chose a shallow DoF to create more distinction between the background and the model.
Getting the flash off-camera can also yield more dynamic results. Here's an example set of images taken from my blog.
Left: Direct flash, Middle: Flash 45 degrees horizontal to camera right, Right: Flash to right front and above camera
The difference in lighting is down to where I place the flashgun in relation to the camera - direction and distance will factor in. You can read more in my blog entry
From a lighting perspective, is this helpful?
What hasn't yet been mentioned is composition; it's the second issue, primarily with the subject being too close to the edge of the frame. It's always better to give yourself a little more space around your subject from the frame edge as you have more flexibility in post-processing with crops. Granted there are times where being close to the edge is beneficial, but certainly not in images #1 and 2. The head and eyes are far too far to the left. #3 balances this nicely with part of the subject off the frame to the right and the head given more prominence at a third intersection.
In fact, the lighting in #3 is acceptable and shows you can, at times, get the lighting right.