From today’s NSI course:

The pretty woman in front of the dystopian death star. The background underexposed by two stops, as usual.

This was done with a softbox on our right, and two more speedlights, on on the right and one on the left.

This was shot in a similar way:

The secret: underexpose the background by about two stops. 1/250th sec at 100 ISO at f/10; and then set the lights to give you those values.