Assume you're invisible.

While there are many ways to stay visible on a bike, it's also helpful to think about motorists around you as oblivious to your presence. Even if it's your right of way, don't assume a car won't cut you off; even if you've made eye contact with a driver, don't bet the farm that he or she won't make a sudden move that puts you in jeopardy. And finally, keep a finger over your brake lever at all times just in case emergency avoidance maneuvers are required... and remember: only the paranoid survive.