Heya, you have wonderful edges here! But you also have several issues with form, facial symmetry and lighting. Here is both a Paintover and a Before and After GIF of it.
On your painting, the first thing that caught my eye is her nostrils. Design based on function is the best principle to follow when it comes to art imo, so based on that, the really small sized slits for her nostrils barely allows her to breath in through it.
Next thing I noticed is the rim lighting. Based on the backdrop, the back light source seems to be coming from below, so only the geometric planes that are facing the ground should be lit up by it.
Next up is her chin. The diagonal plane that separates the underside and the front of our chin has the same angle as the underside of our noses. That means, both of them has to have the same value.
Other things such as her arm here looks flat. Remember that the simplest geometric shape of our arm is a cylinder, so they have to be rendered as such.
I also fixed her facial features based on the beauty standard as much as I could, so hopefully I didn't screw up there :v
Hopefully that was helpful. Don't hesitate to ask me any questions if you have any 
