Tsrip the car down and go at it with 3M Swirl Mark Remover for Dark Cars. If that doesnt work, move up to something more abrasive.

Dont use foam sponges or pads to clean your car, use chenille wash mitts which have a nice depth to them to keep the dirt away from the paint. Also what do you use to dry the car? Try using Microfiber to get off whatever is left after letting water sheet off the car.

Before drying remove the nozel off teh hose, and let water flow smoothly onto the paint, it will sheet off making drying that much easier.

Ounce of prevention..............