By definition, night photography is high contrast photography, rendering output that is frequently low-key. One of your challenges will be to find an exposure setting that allows for enough exposure on the highlights while retaining a rich black background.
Another challenge will be to hold your camera still enough unless you are attempting to capture motion blur.
One annoyance to overcome is that most Nikon consumer-level cameras pop up the flash by default whenever the onboard computer thinks that the scene is not bright enough. To overcome this shortcoming -- you won't want flash -- switch from auto exposure mode or those silly "Scene Exposure Modes" to shutter priority exposure mode [S]. You'll most likely be fiddling with shutter speeds when taking pictures at night. The aperture is likely to be wide open most of the time. There are times when you may want to stop down to increase the depth of field or force a slower shutter speed but for the most part stick with shutter priority.
Many will tell you that a tripod is essential for night photography. A tripod is certainly useful if you can stand the limitations it will put on your technique. Personally I hate them and usually leave mine at home. I like to work fast with maximum flexibility in terms of angle, elevation, composition and have found that a tripod is extra weight that never gets used. All of the photographs taken below were taken without benefit of a tripod. On the other hand, using a tripod will slow you down, forcing you to think through each shot which is always a good thing. Your choice.
An alternative to tripod use is the use of higher than normal ISO settings. Be careful with this. Settings of ISO 1600 or ISO 3200 will boost the sensitivity of the sensor so that you can use daytime technique at night. Such high ISO settings, however, will cause the darkest parts of your composition to be filled with something called "noise". Sensor noise is an ugly beast. Sensor noise will ruin many photographs. If you keep your compositions simple enough, a few bright highlights on an otherwise dark background, it's easy enough to clean up the noisy background at the postproduction stage in a program like Photoshop. This cannot be easily done with a more complex composition, however, or in photographs with intentional motion streaks.
One other concern about night photography: use a buddy, preferably a burly one, to add to your personal security while out on the town.
Let's take a look at a couple of examples.
Moonset over Kitsilano: Taken on a frigid November night with an ISO of 3200 using a 80 mm lens, aperture wide open at ƒ4 with a shutter speed of 1/60th of a second. The cold crisp conditions severely reduced the carrying capacity of the air for moisture and pollution, resulting in sharper than normal points of light on the shore opposite the Stanley Park seawall. By selecting the highlights in Photoshop, feathering a bit then selecting the inverse I was able to delete the background and most of the sensor noise along with it. Then it was simply a matter of replacing that background with a fully black layer. Since I was returning from work on my nightly commute through the park there's a less than zero chance that I would have had a tripod with me. Besides, using a tripod and slower shutter speeds would have captured the movement of the moon and the waves, blurring them and ultimately ruining the shot. This shot works because all of the elements are crystalline sharp.
This shot was taken at the darker, southern end of Kyoto's Kiyamachi Dori. Travelling is hard enough without being encumbered with a tripod. This shot was also handheld [50 mm; ISO 3200; 1/15th second; ƒ5.6], spot metering off the highlights. While not a brilliant photo, I like the simple graphic composition and the subtlety of the light. It does capture a nuance of Japan's mizu shobai or "water business". Not a lot of postprocessing went into this image other than tweaking the contrast a bit.
Also handheld, this shot of a Ferris wheel at Vancouver's Pacific National Exhibition was taken with the following specs: 10.5 mm fisheye; ISO 200; 2.5 seconds; ƒ22. As you can see, I switched to aperture priority [A], stopping down to reduce the amount of light, allowing a longer exposure so that the movement of the ride could be captured without blowing out the highlights and still allowing a rich black background. Note: Wide angle optics tend to limit camera shake; telephotos to over-emphasize it. Again, little postprocessing was required.
Painting with Light: same settings as above except that I used a longer shutter speed of 7.1 seconds, consciously moving the camera to paint streaks of light across the sensor. This kind of motion photography requires plenty of trial and error. On the other hand, experimenting is always fun.
All photographs were taken by Brian Grover.