Bicycling advocates stress the following safety precautions when cycling:* Wear a helmet. Today's helmets are lightweight and well-ventilated; every cyclist should wear one. * Ride with the traffic, not against it. * Obey the same traffic rules as other drivers do. Cyclists should obey traffic lights, signs, and traffic rules as do automobiles. "By law bikes are supposed to obey the same rules as cars," says John Allen, president of the Boston Area Bicycle Coalition. * Use proper bicycle hand signals for turns. * Have reflecting lights for night riding. "It's really essential to have a rear light and a headlight," says Marcia Lowe, senior researcher at the Worldwatch Institute in Washington, D.C., and author of the booklet, "The Bicycle, Vehicle for a Small Planet." * Try to anticipate what drivers are going to do. Drivers don't always see bikers in traffic, Ms. Lowe says. "Skill is the basic problem because a very large percentage of the American population has had no training or instruction in bicycling beyond what they learned as a child from their parents," Mr. Allen says.