Dishwasher Dos and Don'ts. From Martha Stewart
DO use only the recommended amount of detergent -- too much can leave behind a residue, and too little can result in dirty dishes.
DO run only full loads. If the dishwasher is partially full, use the Rinse-Hold cycle to remove odor-causing foods. This is more economical than rinsing dishes by hand, which can waste up to 20 extra gallons of water per load or 6,500 gallons per household each year.