What i'd suggest to begin with is leave your camera on fully auto, turn your flash off and use a tripod or steady surface (such as, well.. the ground) - of course, so there's no blur. Your camera will know it cannot compensate for low light by using the flash, so it'll adjust the iso/shutterspeed/aperture accordingly. Once you've taken a few shots on auto, you'll see what shutter speed and aperture it's using and the effect that's creating: from there, you can make slight adjustments so as to get your desired effect.
These are some spontaneous portraits i took the other night with a friend, we'd just gone for a walk (with a ukulele
), I saw the moon was out so i told him to sit down. it was taken with a dodgey happy snapper; fully auto, just resting on the ground to rectify any handshake.
and another, streetlight in view
they were both at 1" exposure