Rinse and dry all greens. They'll be fresher, crisper and safer to eat.
The darker and more bitter the salad green looks, the better it will be for you. Mix strongly flavored and colorful greens like arugula and radicchio with milder greens. The popular tricolore salad---made with arugula, radicchio and endive---follows this model.
Don't forget about herbs in your salad! Basil, cilantro and parsley are all great when added to a salad mix.