You got the details of the eyes down, but I have some things to suggest.
Take your reference, turn it black and white, then blur it to simplify values.
However, my suggestion to you is to simplify the values and up the contrast. Sometimes color can get in the way when you're trying to turn something from color to black and white.It helps to remove color from an image then blur it to see the gradation from lightest to darkest.
Group your darkest darks and lightest lights.
See if you can replicate a rectangle similar to the value gradation with pencil. (B grade leads are the softest and are wonderful for making the darkest darks whereas H grade leads are better for lighter areas of value.) But you really can use any lead type as long as you're careful with the pressure you use to push down on the pencil. Once you're done getting the hang of that, see if you can group and simplify the shadows like you're cell-shading.
Texture and highlights usually go last, especially when it comes to hair. (At least from my experience.)
I notice you're placing to many strands on the hair. Hair strand texture usually comes last. (And I guess highlights too if you're using an eraser putty.
Pay careful attention to the overall structure of the face.
I notice he has puffy looking eyes. Err...a bit of shadow under his eyes. (I think there's a korean makeup trend for that dunno what it's called again.)
I think you could add the smile lines by his cheeks, darken the corners of his lips, shade the lips a bit to emphasize the highlight of the bottom lip, and darken that little area under his chin and just above the collar of his shirt.