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An attractive girl in an okay pose.  Her facial muscles are in neutral waiting for a reason to be otherwise--but still, nice features and great hair.  The bottom is high-key and the top is low-key---the eye goes to the brightest areas first and that is not your center of interest---her face is the center of interest.  I made some quick and unfinished changes to your image to give you an idea of what I mean by not mixing high and low key and by including clothing and props that have color harmony.  I used the burn tool to tone down the arm and slim her face slightly.

Here is a high key example of your image.  The eye goes to what is different in the image which is her flesh tone.  In a low key image the eye goes to the brightest thing in the image which is also her flesh tone.  The center of interest is maintained in both high and low key.  I hope this is helpful.

John thank you very much for the explanation and the demonstration interesting!
I take note!