So let's say you have a photo shoot for a headshot and you do not have a makeup artist and can't afford one. Well here are some tips:
What I would do is put on your foundation/powder, and then go to Sephora or Macy's -and have them do your eyes, your eyes are the most important part of the face to capture so have them enhance your eyes, or give you a light smokey eye and then purchase the shadow or mascara. A light gloss or chapstick is good enough for lips for a headshot, otherwirse ask to get a lipstick done too and buy the lip-liner, you can always fill in your lips with it later if you need a touch up.
Or if you do not have a powder then go to the makeup counter looking for one that is long lasting. A good powder to make your skin look pretty is very important for a good headshot. (I personally feel ready for the shot just knowing my foundation base is good.) You could bring your own fake eyelashes to the counter, or ask the makeup artist to suggest one. But remember the makeup artists at the store are also sales people so be prepared to purchase something if an artist is doing your eyes, or helping you with something. However this approach can be less expensive than hiring a makeup artist if you are broke.
Another tip is to bring a photo in with you from a magazine editorial that shows the look you are going for.
As for hair, I would blow dry it to give it volumn but you want to look natural in a headshot, like you do typically on a normal day so nothing drastic. Just be you. Or get your hair cut or trimmed the day of the photo shoot for fresh feeling hair that was recently styled.
Warning for getting makeup done: Don't say you have a photo shoot, they might over do your makeup, just say you have a date or an interview or something, because sometimes makeup artists over do it.