I'll point out anything I can.

Unless you're aiming for a realistic look, I think that the eyes are a bit too large, though it does fit a cartoon-ish style if that's what the goal is. The piece would look more pulled together if, when detailing the neck, you kept the dither-shading a little bit consistent. The nose (around the bottom/in between the nostrils) looks very thin compared to how much the nostrils protrude.

That's all that stood out to me, I hope I'm not looking too much at stuff that you're purposely keeping.

This is a self-portrait sprite (with exaggerations) on a project I'm working on, there will be either one or three other sprites I'll be making to go with it on a fighting-game like screen with a background showing a classroom and my teacher eating with his legs up on his desk.  It spawned out of a joke with my friend and I, that either it would be us fighting each other or us vs. two other girls in the class we joke with.

Anyways, enough of my rambling and on to the point. I've reached the part where I'm not sure whether to start adding details yet without some input. Are there any obvious proportional/anatomical problems? None are sticking out to me, and as for muscle and such, I'm not trying to make the sprite appear strong or anything, so I want to retain the thinness.

Also, whoops, I should add that it's a female, so I'm kinda hoping that when I add detail it doesn't take away from the femininity!