The most important thing, even before attending to the materials, is to have the eyes doing something. Unfocussed eyes looking vacantly into the distance make their owner look dead really quickly. The human eye - your eye - is very sensitive to what other people's eyes are doing. So. Add a prop to your scene - any of the standard Poser props is fine, because you now make it invisible. Set each eye to 'point at' this prop, and as you move it around, it makes adjusting the eyes much more controllable than with the dials. Also, if you want your character to look at something or someone in the scene, position a camera at that place while you adjust the eyes. Subtle variations in the position of the head and neck can make a difference too.