Put a capful of soap into a bucket filled 3/4ths with water. Use a garden hose to rinse as much dirt as possible off the car.
Use a bucket and sponge to wash the car, being careful to not get the soap on the roof. The car should be hand washed, not washed at a commercial car wash. This way, care can be taken to be sure the soap used to the wash the car's body doesn't get onto the convertible top, which can damage it.
Wash the car's convertible top infrequently. The cover of a convertible does not need to be cleaned as often as the car needs to be washed. You may only need to clean it about twice a year. However, large pieces of dirt and bird droppings should be cleaned off immediately. Bird droppings are acidic, as well as unattractive to have on your car. In many cases, dirt and other stains can be removed using water and a soft cloth.
Clean the rear window with a soft cloth and plastic windshield cleaner to prevent damaging it. If your rear window is plastic instead of glass, you should keep it clean so that it stays clear and easy to see through. Don't use harsh chemicals or products intended for glass on a plastic window, since such products could damage it.
When it's time to clean the top, park the convertible in the shade. Buy a gentle, pH neutral cleaner that is intended for convertible tops.
Use the convertible top cleaner on areas where it looks especially soiled. Apply it with a soft cloth, then rinse it off thoroughly. To prevent mildew and mold, you should allow the top to dry completely before folding it down.
When the top is dry, apply a convertible top protectant, to prevent the top from fading or cracking, and to help it repel dirt and oil. That will keep your convertible top looking new. Cloth tops may need a product with fluorocarbon repellants. For vinyl tops, it is more important to get a product that will repel UV rays from the sun.
Apply several even coats to the top of the convertible, allowing each coat to dry for about 10 minutes before applying the next coat.