According to About.com, the easiest way to clean and maintain granite countertops is by dusting the counters off and then wiping them down with water. The best way to dust a granite countertop is with a microfiber cloth.
Another way to clean granite countertops is with stone cleaner specifically designed for granite. Stone cleaner helps remove stains that water does not always remove. A paste of baking soda and dish soap can be used to remove tough or oily stains on granite. Mix 1 cup of baking soda and 5 tablespoons of dish soap together. Place the paste on the stain, cover it with a sheet of plastic wrap, and allow it to sit overnight. Gently wash away the paste with clean water and a rag.