As a working newspaper photographer, probably one of the things I am tasked to do everyday is to take a subjects portrait for publication.
It would be great to have the whole day to scout out a great location and then meet the subject there at sunset when the light is just perfect; however the reality is I generally only get 15 minutes of someones time (if I'm lucky) in the middle of the day, when the light generally isn't going to produce portfolio type work. The locations are also usually determined by where the subject is going to be at that particular time of the day.
This is where, as photographers, we have to make the best of a location, and work with the light that is available at that time of day to create great portraits.
Even some of the worst locations I have showed up at, you can usually find something there you can work with. I usually am always scoping for a plain backdrop - maybe a textured wall in the hallway - or the side of a building that you saw on your way from the car to meet the subject. The more plain and less cluttered the background, the better, you want your subject to be the central focus of the photograph.
It's also good to know cool locations in your city and make a mental note of them so you can bring subjects that live close by those locations there quickly. I am constantly driving around between assignments looking for cool spots.
Recently I had one such assignment with playwright Ryan Van Horne. I met him at his house and we drove a few blocks over to a local park, which I knew had some good places to work with from previous shoots. I choose a nice plain wall for a backdrop and got Ryan to lean against it. It was about 4 pm - and the light was definitely nothing to write home about. I chose a part of the wall to get the subject in the shade - which is a good first step for "bad light" portraiture.
I decided to add some flash as a key light. I like to travel light and am definitely in the "Strobist" camp - I almost exclusively use speedlights to light my subjects. I like size and portability you can get from using a flash. I use the Pocket Wizard Mini TT1 on my camera to trigger the Pocket Wizard Flex TT5 on my flash. These are great units, and although they have the ability to operate with the camera TTL, I almost always use them with the flash in manual mode. The added benefit is that they high speed sync - which means I can set my camera to any speed higher then the usual flash sync speed of 1/200th of second on camera.
In this case, in the shade, I set my camera to 1/500th of a second at around f4, which underexposed the background slightly. I then played with my flashes manual output settings to get the look I wanted. In this case I was trying to mimic the look of the sun, so I used direct flash with no diffuser. Sun is a harder type of light, so the small flash does a good job of that.
I also added a CTO gel to the flash to warm the flash up slightly, something that happens near the end of the day with the sun. You can get sheets of coloured gels at any movie equipment store, they are generally pretty cheap and you can cut them up to fit your flash.
This is a pretty easy technique, but it is something you can use (but don't over use) in your photography. It's pretty a pretty powerful thing to be able to make the sun set on command!