Every corner of the car sits on the road different. Because of this, your tires will wear in different ways. They will develop wear patterns the more miles they get. There are several ways to rotate your tires. It will depend on the way your car is set up, the settings of your suspension, the alignment of the axles, and also the specific rotating direction of your tires- (some tire manufacturers make tires that are only supposed to travel in one direction. These are generally high performance tires, and specialty tires, for example snow tires).
The best way to figure out what the proper rotation for your car, is to consult your local tire specialist, or the owners manual from your car.