The recent Halloween Challenge highlighted the need for a smoke tutorial and here it is:-
General whispiness can be achieved by dragging the Slash, Pinch, or Standard (with a suitable alpha) Brushes across a subdivided poly plane, set just in front of the camera and bleeding beyond the edges of the canvas.
Specific, crisply defined threads of smoke are created by drawing out ZSphere chains, converting them to polys and flattening them in the Z axis. This flattening helps determine how transparent each of the smoke strands are.
For all smoke SubTool elements, turn on BPR Transparency in the Tool Display options and apply the FlatSketch material to them. See attached images for edit details.
Transparency needs to be turned on also in the Render Properties panel.
The nice thing about making your smoke in ZBrush and not relying on stock photos is that you can draw the smoke exactly as you want it, even forming it into the suggestion of ghostly faces.