Drawing the mouths is just like the nose. With the nose and mouth it is probably best to get some anime pics of my site or elsewhere. Note mouths can be just simple lines.
 
These are front on pics of some mouths.
sorry about the shabbiness but I do these very quick. These are profile views of mouth, there are also some noses in there to.
 
 
 
 
Here are some mixed mouths.
 
 
Notes: Lady's mouths are allot smaller than men's.