The lips

 The lips are made by selecting the relevant edges around the mouth in sub-object mode. By holding shift and moving the edges inwards and upwards, new faces are created. Doing this twice for each lip will create a shape similar to the image below.

 

Once all the vertices have been positioned, re-activating the turbosmooth modifier shows the end result. Also, while at this stage, the chin can be reshaped and the bottom lip more defined.

While making models like this, I am constantly tweaking the whole face to improve the flow. Noticing issues that need to be fixed early on helps in later stages. The red lines on the image below show an uneven surface that I am not happy with. This isn't as catastrophic as some pinching caused by having non-quads in the mesh, but annoying nonetheless. Further vertex adjustment will fix this.