So far I'm just drawing celebrities and models from reference, and trying to figure out what makes their facial structure different. After I do maybe between 50-100 of those and can knock them out in 5-10 minutes no problem I'll be moving on to some caricatures. Depending on how that goes I'll do a bunch and move on to completely original character designs of women.
That being said, here's the first batch of attempts. Most are the Transformers chick Megan Fox, with a couple of Adriana Lima (aka some crazy skinny super model), and one of Aeon Flux herself, Charlize Theron.