Using a flashlight to paint your images during long exposures can leave you with shots full of depth and mystery. Allison Earnest recommends starting with a 15-second exposure at f/5.6 and turning on noise reduction.
Let your camera focus before turning off all of the lights and firing the shutter. Use a flashlight (Earnest recommends INOVA) to quickly paint over your subjects. Keep the flashlight moving while turning it on and off in short bursts.
For a detailed guide, check out Earnest’s article, Painting with Light, at Imagininginfo.com, or her book, Sculpting with Light.