Place a refrigerator thermometer in your fridge overnight and check the temperature in the morning.
Adjust the setting on your fridge if the thermometer reads higher than 38 degrees Fahrenheit or lower than 36 degrees Fahrenheit.
Leave the thermometer in the fridge overnight again. Check it in the morning and continue adjusting as necessary until you reach the right temperature.
Dab your lettuce with a paper towel to remove excess moisture. Place it in a plastic refrigerator bag with a zipper seal and make sure all the air is out before sealing it.
Move the lettuce toward the bottom of the refrigerator. Keep it close to the front of the fridge, since cold air enters along the top of the back. Store the lettuce in the crisper to avoid the coldest air.