
I have always loved night photography - the interplay of different light sources produces a fantastic array of colours, and the contrast between light and dark areas creates a vibrant, engaging scene. I do first was:
1. Location and Viewpoint
Choose a shooting location that will make some interesting shaped light trails, and maybe choose somewhere with plenty of traffic so that you get lots of car trails. Picture the cars in your mind moving through the scene and imagine how their light trails will look.
2. Car Direction - Towards or Away?
Think of of what you want to take a shot a car that towards you or away from you. When choosing your viewpoint think that car lights have different colours - white at the front and red at the back. The color of the light trails in your photo can dramatically affect the feel of the image.
3. Plan Your Exposure Time
This is very critical when photographing car trial at night.. Longer exposure means more trails and their length extended but if it too long its faded and that's very noticeable..

I hope this helps...