Eyes will forever be hard (for me, anyway) and will probably take lots of practices to get it right.
I really recommend looking up tutorials, especially in devart! I used to look up tutorials in google and thought I've found some good ones but.. the real artists are at devart. xD
I've favourited a few myself from there:
http://blaaaaaaaah.deviantart.com/favourites/#Tutorials
Though I'm sure there's more.