I think one thing that can really add interest to a piece is a background, even a blurred one, because then you have things like bounce lighting to take into consideration. When you have just a plain solid background, there's nothing that's giving the storytelling elements, like @pifalo mentioned in their comment. You also may be dealing with some "flatness" when it comes to your shading and values. Have you tried looking at the image in black and white? This is very helpful for seeing a value map of the piece.
yeah the black and white check helps, maybe deepen the shadow on the hair and one side of the face first so she reads less flat even before you invent a whole background
