A faulty or leaking refrigerator door seal wastes energy. If the seal is dry and cracked, if you see condensation (water droplets) around the edge of it, or if your refrigerator is not staying as cold as it should, you may need a new seal. Leaks can also increase your energy bill and stress your refrigerator, shortening its life. They can also promote mold growth.
Order a replacement door seal. It's easy to find them online. Make sure to check the model number for your refrigerator when you order it. When it arrives, hold the new door seal up against the old door seal to compare the size. The sizes are rarely incorrect, but it will save you the trouble of doing the job twice if you happened to receive the wrong door seal.
Remove the old seal. Once all of the screws are loose, the door seal should easily slide out from behind the plastic liner. Don't be too forceful when doing this step, since some plastic liners can be quite brittle and crumble if you are too rough. If the plastic is old, replace it.
Apply powder. Use a bit of baby powder or talcum powder to prevent sticking. Rub some powder around the hinge side corners of the door seal, and where the seal slides. This will help to prevent the door seal from twisting as it meets the metal of the fridge. If this still doesn't prevent twisting, then wedge a screwdriver under the seal as you close the door and leave it shut for an hour.