Often simpler is better. Here's a headshot of a young executive, using only natural light without any reflectors or fill-in flash. The new trend seems to be to have a background that "looks like I'm in the office" 😉 instead of your standard studio background .

I had my subject stand 1 metre inside a doorway facing outside, so that he was in covered shade, yet still getting most of the light from the front to illuminate his eyes and eliminate those dreaded racoon eyes when shooting in uncovered shade. The light fall off shooting from outside into the room was quick producing a dark background, yet with some detail.

If the light, looking from inside to outside is a bit bright for your subject, have someone hold a dark towel up behind you to minimise squinting, although as Perter Hurley says, a little bit of a 'squinch' is good. Don't forget to set your white balance by using a grey card or an Expodisc.

To give the subject an alternative look, I moved indoors, bounced the on-camera flash backwards over my left shoulder, off a white ceiling

but had him turn his left shoulder closer to the camera this time - very different look, but just as quick to set up