One tip for helping to figure out topology for lip area is to sketch out separately a rough range of movement of lips. Then in ZBrush i used claybuildup brush to mark the major areas:
Then i later used ZBrush zremesher guide brush to help mark loops in important areas:
Another tip is to quickly test the lip corner for a smile and inner brow in to see if facial topology is working okay. Later this topology will need to get simplified greatly before beginning on facial deformations.
Hope you find this helpful.
original concept, design, model
Nicolas Zinovieff (his Highlight tool i'm finding very helpful in sculpting with ZBrush and using ZBrush custom zapplink properties custom view to quickly flip between drawing and sculpt)