Defining detail for the lips

To make the lip, the edges were selected around the mouth opening and whilst holding shift the edges were copied. Switching to the vertices tool each vertex was aligned to the shape on the reference images. To give the lips some depth the edges were copied again and pulled back into the mouth twice and scaled down with the scale tool. The edges were then copied down on the bottom lip and up on the top. Wield was used to ensure that all the vertices were joined around the inner edge of the lip.

The detail on the lips looks more realistic after turbosmooth has been switch on.