A cityscape is basically an urban landscape. Instead of mountains, hills and forests, you photograph tall buildings and bridges. They date back to 17th century painting in the Netherlands, so they aren't a product of photography as some might think.
Cityscapes, like landscapes, require scouting for a good location and waiting for the perfect light. The beautiful images you see on postcards are taken by photographers who wait until the light is just right. Many spectacular cityscapes are taken at night, especially in large cities where the lights are impressive at night. Long exposures are also a good way to capture night time cityscapes. Highways and streets with intense traffic are ideal for such shots.
The same rule that works for most natural and available light photography genres also works for cityscapes: be there when the light is soft, either early in the morning or at the end of the day.
Share your impressive cityscapes and check out the work of others.