Always Double lock your car when entering or leaving it.
Mark your car radio and other removable car equipment for identification.
Utilize a locking switch lock.
Never leave valuables such as chequebooks, credit cards, etc, unattended in your car. Lock all valuables in the trunk.
Park in a well-lit and busy area.
Carry your vehicle registration with you. A thief can use your registration to show "legal" possession of your car.
Report suspicious actions, someone peering in to every parked car on the street, someone forcing a vent window or removing gasoline or, license plates.
Check the back seat before getting into the car.