Nice start. Shading is hard.
A couple of prominent lines are too high.
The eyes should pretty much be a circular shadow, with the brow more or less straight. You’ve got too little shading under the eye and the shading under the brow is too high and pointed (remember, make it straight[ish]).
THe other prominent thing is the cheekbones. Again too high and this time too straight. They should be more ‘v’-like.
The lips should also have greater definition and the shadow under the nose just a little longer.
The reason for all this is that the light for the rest of the scene seems to be directly above and in front of the forehead, while the shadows at the brow and cheeks suggest a stronger light that is more directly above the head. The incongruity makes it pop.
I like the clasp at the neck. Looks like a metal ring and glass. Nice!