You're onto the right track, I guess. Remember that eyes are round balls, and the shading should reflect that. The iris is circular, but not bulging as much as the eyes does - however, there's the cornea in front of it, which follows the round shape of the eyeball, and it's the cornea that often reflect light sources (the white shape, or shapes, on the eye). There's usually some flesh and veins showing in the inner corner (towards the nose) of the eye, and the skin wraps around the eye (rather than onto the eye).
As for the eyebrow, people come in a lot of different shapes and colours, but your eyebrow is looking a bit too low for an average human - unless you're not drawing from a directly in front perspective.
Anyway, use references as much as you can, paint a lot and have other people look at it - often, at least for me, when I draw, I am somewhat blinded from my own mistakes, because I grow familiar with my painting. To counter this, flipping the image might help, but in most cases, the best feedback is from other people.
Good luck, the human face is truly an amazingly intricate subject to paint, and draw.