To clean most greens, you can just rinse them in a colander under cold running water to remove any dirt. Be sure to separate the leaves for thorough cleaning—nothing is more annoying than a gritty salad. For greens that tend to be very sandy—which is anything you buy at a farmers’ market or is otherwise freshly picked, and even unbagged spinach and arugula in the supermarket—first plunge them into a sink or dishpan of warm water; this relaxes the leaves, loosening the dirt for easier rinsing. Then lift the leaves to a colander and rinse under cold water. If the leaves are still limp, crisp them in several changes of cold water.