3. Understand sources of light
First thing’s first, you have to be able to read the ambient light in your environment. You have to understand what is the approximate length of time that you will likely have to keep your shutter open in order to get an even exposure. This is how you will lock in your exposure settings.
Tip: It’s not a good idea to rely on your camera’s histogram when shooting at night, so I recommend simply taking lots and lots of test shots until you dial everything in. Once you have calibrated your shutter speed and aperture, now you can start looking at the other sources of light that you can use to your advantage.
One of the coolest ways to take long exposure night photos is through the use of light trails – the movement of a source of light through the scene. In order to capture light trails, you have to consider your various light sources, and understand how their movement throughout the scene will affect your final photo. This could be cars, stars, a flashlight, lanterns, etc.
Long exposure night photography with light trails requires a lot of pre-visualization in order to be successful; you have to try and picture your final scene before you even set up. It’s difficult, but it can produce amazing results.
4. Capture multiple objects in motion
In the above photo that I took in the Marin Headlands, above San Francisco, California, I was able to capture two moving subjects that left light trails. The stacking of multiple 30 second exposures shows both the movement of the stars across the sky, and the movement of a ship as it enters the bay.