The other afternoon when I was heating some water for tea and went to the kitchen to check on it there was strong sunlight coming in the window streaming across the stove top. The background was sufficiently dark that the steam from the tea pot was accentuated quite well. This prompted me to grab the camera to see how it would photograph because I'd not specifically shot for steam before now.
So, while I'm certainly no expert on the subject I think the results turned out pretty well here and thought I'd share some thoughts on the process.
The basic ingredients that made this possible were a strong light source, dark background, and boiling water. Specifically, for this shot the sun was coming in through the south facing window with the dark background to the east and me on the west of the teapot. I shot with an 85mm f/1.8 lens wide open in Manual mode focusing on the steam itself in the first two photos above. For the lone cup of tea I focused on the highlights of the teabag because of the lesser amount of steam. Of course, the camera was turned on and the settings were adjusted so that when I poured the water in the mug I was ready to shoot so as to not waste any time and let the steam dissipate.
Here's a few more shots to show the different shapes of interest created by the steam: