Make sure the attendant or valet is actually the authorized attendant. Always park with the wheels turned toward the curb and apply the emergency brake. This will prevent towing. Place valuables out of sight. If you have a garage, use it.
Vehicles are least safe parked at the curb, more safe in the driveway and most safe in the garage.
Lock your garage door. Do not leave your car running while it is unattended. Back your car into the driveway. If you drive forward into the driveway, a car thief could raise the hood to hot wire the car, and it would appear to the neighbors that you were just working on the car. Do not leave the car title in the vehicle.