I decided to have another go at shooting smoke today. I attempted it a few months ago, but I wasn't pleased with the results. I'm happier with what I've managed to get today.
Here's the final image:
This is the original shot, straight out of the camera:
I cropped the image (a square crop worked best for this particular smoke pattern), and then I played around with the contrast slider, blacks slider and tone curve in Lightroom to get the background as dark as I could. I then inverted the image in Photoshop, to give dark smoke against a light background. Finally I brought the image back into Lightroom. I applied the 'purple glasses' preset and tweaked it until I got an effect I liked. Finally, I made the smoke as fluid-looking as possible by reducing the clarity and adding a fair amount of noise reduction.