ajmarti said most important thing.
Expressions looks natural if they affect more then head (it concern to movies and comics). I was really dissapionted when I've seen "Beowulf" and Characters speak with mouth and eyes only. Go to the mirror and try to say somthing not moving your neck.
Moreover in real world symetry does not exist. All faces are not symetrical, all poses are not symetrical. Add some disortion to your figure and Koshini starts look more natural then Victoria.

The rest depends of texture/materials and lights. Poser has great tool "atmosphere" which make scene realistic. Unfortunatelly "atmosphere" make your rendering process VERY VERY long, but if you have few years I recommend try.