Always stop at stop signs and stop lights. Carefully check all cross streets before proceeding (including on-coming traffic turning left).

Even if you have the right-of-way, check cross streets when proceeding through intersections.

Most car-bicycle crashes occur at intersections. Sometimes the car had the right of way and sometimes the bicycle had the right of way (car ran the stop sign, etc.). In either case, the bicyclist loses, so your best defense is to pay attention.