If a driver is parking a car facing downhill, he should turn the wheels so that they face the right side and engage the parking brake. It should be noted that this is for use in the U.S., or wherever drivers use the right side of the road.
This is the proper strategy, whether or not there is a curb present. However, when parking uphill, the presence of a curb makes a difference. If there is a curb, the tires should be turned left. This ensures that if the car rolls, the curb will stop it. If there's no curb, the wheels should face right. In all instances, the parking brake should be engaged.