That depends on what you're trying to achieve with the photo. The quickest way for lowlight photos is to up the ISO, but that increases the amount of noise in the photo. Other ways of doing it include opening the lens/lowering the aperture, but this will great greater depth of focus. Or you could try the shutter speed, but lowering that will blur movement.

The best way to deal with the available light all depends on what you're trying to achieve with the photo.