Shooting at twilight allows the photographer to create beautiful story-telling imagery. The drama of the night sky can make a big difference in how the image is represented. Scout out locations ahead of time, and make a few test shots to figure out the best composition and a few variables. The photograph is your story, a visual narration of what you experience, your interpretation of the scene.
You can see from the test shot below, how much more impact you can create by photographing during more flattering light conditions. The lights on the bridge create starbursts, and the city lights and night sky are reflected in the water. This automatically creates a much more glamorous look compared to the image below.
What's great is that you really don't need anything additional to add to your photo arsenal to accomplish twilight photography. You probably already have a tripod and cable release, or you can use the self timer feature on your camera.
What you might want to do is experiment with white balance. If you have Live View enabled, a feature on many cameras, you can scroll through the various white balance settings to find the most complementary setting. Don't worry about the "correct" white balance, use the one most complementary to the scene. I find 4000K a good place to start. If you are shooting in Raw format, you can tweak this after the fact, which is most helpful if you change your mind!
Since you are set up on a tripod, use the lowest ISO, and use an aperture to create the most depth of field, or to quote fellow BetterPhoto.com instructor Tony Sweet, depth of feeling. You can shoot during twilight almost anywhere, cityscape, landscape, before dawn or after sunset. Twilight can make the ordinary look magical...
Make great pictures! ~ Deb