Totally dark room - *zero* ambient light. Set shutter speed to bulb & lock (if you're able). "Paint the subject" with a light - in this case I used a small pen light. Experiment until you get the feel for how much light & where. Here's a more colorful example - http://www.pbase.com/image/91569664
I bought a 3,000,000 candlepower spot in order to try this outdoors. I'm planning to try our specimen oak late one night - which will probably result in nearby homes calling the police (which won't be the first time). The ultimate night light painting would be to use a really long exposure in order to get star trails as well. Probably will wait until the nights aren't so cold - not a winter project.
For this shot I used a large walk-in closet. Right next to me were my hiking boots - instant subject. This PAD was a 56 second exposure (could've gone longer) and the other example was 36 seconds.
Working hard to get out of a "been there, done that" photography rut.