how can you improving?? well, first of all I need to know what the model (or you)would like to achieve from this image. Technically I like very much the texture of the skin, the high key of the overall image , it's very soft but with all the details very well "painted". From the other side I suppose the model was not relaxed, my first expectation (looking at the global tonality) was to find a "dreamy" image but the model seems to be forced in this position... she's not dreaming , she has only closed eyes and the mouth , in my opinion, seems not natural and relaxed. Ok.... this is the opinion of a man (me) that is not able to achieve half of your image.... :)
In Italy we are used to say : "who is able ...do, who is not able... do critics" ;)
Bye and thanks for your useful trick on the lights. Next session I'll try with the light behind.