Plan in advance your potential routes of escape should an intruder or fire make it necessary. Keep the doors locked and windows rolled up whenever possible. Be alert at stop signs and traffic lights. These are favorite places for assailants to try to jump in. If someone tries to break into your car, pull away if possible, but by all means honk the horn.
Short bursts attract the most attention.
If you think you're being followed, don't go home. Head for a police station, hospital emergency entrance or other safe public place where you can call for help. Park in lots that offer good security, are well lit, and are close to your destination. Don't leave valuables such as wrapped packages or cameras in plain sight in a locked car. Lock them in the trunk.