I got a few tutorials for you that will help improve your portraits in the post-processing. There is something to learn from each of them. One shows that the eye can be multi-colored, other shows that the white space of the eye must also be taken under consideration, and, not as the last thing, you can do adjustments in order to lighen and sharpen the eye to draw the attention to it.
This tutorial shows how to whiten teeth using a Curves adjustment layer in Photoshop CS3. In Portrait Photography, no matter how pretty the model is, how well lighting is and how good your white balance setting is adjusted, teeth may still not be as white and pretty as they should in order to make a picture become a magazine cover. However, this video also teaches that the teeth should have a natural white, which is not pure white. The change is subtile. Before making the change to teeth, do this in order to avoid any other changes of the rest of the image: Duplicate the background layer. Fill the background layer with a gradient that looks like fire. On the duplicated layer, use the Extract filter to remove the girl from the background.