Here are a couple tips that may be helpful that i'm starting to use in practice during facial sculpting.
--I'm finding it really helpful to think about how the narrow shape and a smile shape work with the lips. One reason this is really helpful to test is because of the large distance the lip corner needs to move between these shapes (could be huge for a more stylistic style character).
--Have an idea for the facial expressions will eventually want to make even during the early modeling stage. For example is there room for the brows to go up, when the lip corners go down is there still some cheek room, how to separate the nose from the lip.
--i want to soon begin applying these facial sculpting techniques to body deformations, where i can think of a deformation like a facial sculpt and figure out what extreme shapes to try for shoulders/hips etc. (on the side i did a quick test using a lattice to simulate like the shoulder was skinned, so i could in a couple minutes see how the shoulder topology is working)
Hope this is helpful,