Discard any wilted outer leaves. Prep and wash greens as directed for each type of green.
For leafy lettuces, such as green or red-tip leaf, butterhead, and romaine, as well as endive, remove and discard the root end. Separate the leaves and hold them under cold running water to remove any dirt.
For smaller greens, such as spinach and arugula, swirl them in a bowl or a clean sink filled with cold water for about 30 seconds. Remove the leaves and shake gently to let dirt and other debris fall into the water. Repeat the process if necessary. Drain in a colander.
For iceberg lettuce, remove the core by hitting the stem end on the countertop; twist and lift out the core. (Do not use a knife to cut out the core, as this can cause the lettuce to turn brown). Hold the head, core side up, under cold running water, pulling leaves apart slightly. Invert the head and drain thoroughly. Repeat if necessary.
For mesclun (a mixture of young, small salad greens often available in bulk at farmer's markets), rinse in a colander or the basket of a salad spinner (see photo, directional).