What settings on your camera should you use when taking photos in dark environments?

Such as these http://browse.deviantart.com/?qh=&section=&global=1&q=ifc+roof#/d2ux6yt

when you are taking photos of a model in that type of environment where it is dark but is lit up by light, what are the best settings on your DSLR to use (i have a nikon D90) in order to create interesting lighting?

Thanks.
>>> What settings on your camera should you use when taking photos in dark environments?