Actress Headshots
I think a female headshot should present the image of a smart, confident, woman who wears no make-up and looks great in any sort of lighting. And she's sexy in a 'I am not trying to be sexy' sort of way.
A woman's headshot has to show off and emphasize feminine features, and the particular aspects of the female face that make it beautiful in its own way. This means emphasizing eyes, or jawline, or hair, or in many cases body (hard to do with a headshot but possible), as well as bringing a sense of balance to facial features... big eyes are great but a headshot can look like a kitten poster if those eyes are hovering over a tiny mouth.
I cannot emphasize enough that make-up should look natural. Natural clean skin, nice eyes - this is what a director wants in a headshot. If you must line your eyes don't line them thick and dark - this makes your eyes look small and beady usually. And don't use lipliner - it makes a face hard and mean looking.
Pay a lot of attention to the way clothes look around your neck and bust. If you've a lovely neck and shoulders you'd be stupid to not highlight that. If your neck is shorter or a little thicker, consider a v-neck, which will make it look longer. If you've a bigger bust then dress such that you don't look dumpy and lumpy. In general, go for simpler clothing - no distracting patters or lots of frilly things around you neck.
Jewelry can enhance or seriously distract, depending on the flashiness of it. The human eye is attracted to light and sparkles, so while those huge Swarovski crystal earrings your friend made you might look great, the people looking at your picture want to see your eyes not your earlobes.
Hair... there is so much to be said about personality through hair. Hair should look alive and like it hasn't been worked on for hours.
Remember, people casting things are acutely conscious of time because time is money. If your look is one that appears to require precision maintenance, subconsciously the person doing the casting is going to think you're a primadonna and a lot of work to have around. The last thing anyone in the entertaiment industry is interested in is a person who isn't easy and fast to deal with.