I think most everyone may have figured out how to achieve good results taking smoke photos before I did, but just in case here’s my setup. The most obvious observation is that you want to maximize contrast — I used a matte black background to aid definition. Next, you have to light your smoke, and this was really the only tricky part. I remotely triggered a flash at left, and had a reflector (tin foil) at right. There are many more complex ways to do this (light boxes, multiple strobes, etc), but this was quick and easy and it let me experiment within about 2 minutes. The thing you want to note is that you need to control flash coverage; I would recommend either a snoot, or to zoom your flash. Fairly proud of the results for a first try.
Here’s another perspective to see the simplicity (*another note, also I think incense might be a bit easier than matches.. but I didn’t have any around the house).
More creative things to do. After you have your shot, you can invert the colors (i.e. black to white, as below, etc), add color, clone, twirl, or do a number of things to make your art. More examples here.
Well, there’s more to be done. Next I think is dry ice, more smoke, some props, and maybe to gel the flash. I had fun, though. =]