I think your struggeling because you don’t have a basic understanding of how to get things done in Zbrush (i’ve been there, believe me).
I think it might be good to go around and look up some video tutorials on how to get the basics of the head done, which brushes might come in handy and such
it’s hard to explain in text how to go around and fix certain specific thing in your model, because for me it’s allways trail and error, just forcing yourself to go messing around with the claytubes brush for an hour can really help in finding out the particular uses this brush can have.
There are many different ways to use one and the same brush, try for instance stroking, quickly releasing, stroking again…this’ll have a different effect than for instance, stroking, holding and going over the same stroke again. Try horizontal stroking followed by vertical stroking, this can have different kinds of effects. It’s very much just messing around and keeping your eyes open for how you get to certain results.
I realise this might all be not direct critique to your model, but as I said before, I think you need to get the fundamentals down a bit better.
ps. I just did a quick youtube search for Zbrush + eyes, came up with this:
Free Sculpting Tut
I quickly went through it and it can be of help I think (even though the quality of the stream is quite poor)