Our 'second pass' continues into the lower half of the face: the mouth and lips.
Again, a sense of the anatomy is vital to getting the shape of the mouth right. I'm overviewing as we go along but ask yourself: do you understand why the mouth is shaped as it is? Or why the upper lip is further forward? Or the relationship between the ends of upper and lower lips? If you are not sure, there is a load of information for artists 'out there' to look at.
Remember: You can't have too much preparation but you can have too little...