The problem with using long exposures is that you may shake the camera, resulting in poor pictures. The way around this is to use a tripod. You either use the shutter-release cable if your camera comes with one or use your camera timer.
 
Tip 2: Take Control Shots

One problem with digital cameras is that there are always some pixels on the image sensor which are bad. When taking day photos, these defects are not discernible. However, they are pretty obvious in night photos. How do we correct these? Here’s a simple way – take a control shot, then use image editing to subtract out those bad pixels.

This is how it works. The next time you’re out to take night photos, go ahead and snap a picture of Scene A, as you normally would. Then, when it’s convenient, take a photo of the exact same Scene A again, but with the lens cap on.
 

Now you will have two images, one night shot and one control shot (with the hot pixels). Load them up in say, Photoshop. Switch to the control shot and select Edit and Copy from the menu. Next, switch to the night shot and paste the copied image as a new layer. Then, select the new layer and change the Blend Mode to Difference and click OK. You’ll get the correct night shot with the hot spots subtracted out.