Check your camera’s LCD and histogram after taking a picture. Do the shadows have detail, are any of the highlights blown out? The histogram is the best indicator you have out in the field to determine proper exposure. Remember that the left hand side of the histogram indicates the shadows, the middle indicates the midtones, and the right side shows the highlights. If the graph is bunched up on the left or right side, your image is under or overexposed, respectively. Use a good balance of shadows and highlights to add extra contrast to your night time images.
In the above photo, you can see a perfectly blended exposure of the sky, houses, boats, and water to give good contrast yet retain plenty of detail in the fore, middle, and background.