To keep romaine lettuce fresh for as long as possible, take it out of the bag it came in, dry the leaves as much as possible, and then wrap them loosely in fresh paper towels. Place the wrapped lettuce in a re-sealable plastic bag, removing as much air as possible. Store it in the produce drawer of your refrigerator, where it should stay fresh for up to two weeks.
If the romaine lettuce is not pre-washed, separate the leaves and place them in a large bowl filled with cold water. Swish the leaves around to remove any dirt, then drain the water. Rinse each leaf under cold running water. Place the leaves in a salad spinner, and spin until the leaves are dry. If you don't have a salad spinner, shake off as much excess water as possible, then lay the romaine lettuce leaves on a clean, absorbent kitchen towel, and pat dry with paper towels.
For storage, lay out two or three fresh paper towels, still connected, and spread the lettuce leaves out on them. Roll up the lettuce leaves in the paper towel loosely, then place it in a large re-sealable plastic bag. Gently press on the bag to remove as much water as possible before sealing. Place the bag of romaine lettuce in your refrigerator's produce drawer.