One tool that we have to improve our camera's low light performance is "bright glass". By that I mean a lens that has a very large aperture such as F/2.0 or larger. There are now lens, even for the small compact cameras, that are as large as F/0.95. But typically you will see F/1.8, F/1.4 or even F/1.2 lenses available for your camera. You can pick up a fixed length lens, known as a prime, for a very reasonable price.
I've seen a photographer, Aaron Wallace, working with a model in the streets at night using nothing more then his iPhone as a light source. He was using his Olympus PEN with an F/0.95 lens in place. A large aperture lens allows a lot of light in and allows you to work in much lower light. They do wonders and give you such incredible Bokeh, see the lights behind his model?
But like all things in photography there are always trade offs. And in the case of portraiture the narrow Depth of Field (DOF) created by an aperture that large, is very narrow. DOF is the area... a band that is in focus where you hope