
eye shape and eyebrows are good to play with. the way the eyebrows are pointing... the shape of the eye... sometimes it depends on the shape of the face... weird eh? and the mouth: if it is smiling, you have to find the right position and also have the right length and stuff... just a bit more practice with be great.
i also like to see other peoples work and examine it so i can get some ideas, so i suggest you to maybe... idunno watch more anime? ; D read more manga? pay attention to the facial expressions, maybe jot them down. its easier for me to remember eye shapes and mouths when i draw them and not just try to remember it.
hope i helped!