I have always tended to do most of my photo's at night and have dabbled into playing with light trails in the past. But recently I have become addicted to shooting this style.
As with most photography its location, location, location! Once you find a good spot its all letting your creativity loose.
I highly recommend playing around with it. How do you do it? Well of course you need your dslr or camera that shoots in manual and a tripod is highly preferable.
After you find your spot. Set the camera up for a long exposure shot (these photo's were shot with the settings, first photo: Shutter 15 seconds, f14, iso 100 sexond photo: shutter 30 seconds, f22, iso 200).
Then its all trial and error lol play with it, get some great shots and above all. Have fun with it!