Wash the lettuce well under the tap, I will always petal by petal, dry the lettuce in the salad spinner, grab a big plastic bread bag and do all the lettuce in there. Keep the bag open, swinging through the air and lay there like a knot. Now you have a kind of balloon filled with lettuce. Put it into the fridge, so the salad days remains good. You can also continue to play a bit of lettuce and then close it again in the same way.