The below tips for caring for paper based playing cards were taken from Lee Asher's Jerry's Nuggets card care guide. You may not be an owner of Jerry's Nuggets but Lee's guide is extremely useful and appropriate for any type of paper based deck of cards. You can download the guide here: http://www.leeasher.com/store/playing_cards/gift.html
Storing your playing cards
Be careful to avoid storing your playing cards in an attic or basement. Why? You're looking to avoid potentially higher levels of humidity, moisture or even damp. Exposure to consistently high temperatures is also a good thing to avoid - so don't stash your decks in a box next to the radiator!
Over time, consistently high levels of humidity or moisture may contribute to your cards potentially warping slightly. Storing your decks in a cool, dry area of your house is advantageous and a well-ventilated room is even better.
Handling your playing cards
Sounds like common sense, but washing your hands before use can really help your decks. Lessening the chance of dirts and oils from building up on your cards can really help prolong their life. If you're handling your playing cards for a decent amount of time, you may want to consider washing your hands at regular intervals - especially if you're doing springs, fans, faros or shuffles.
Cleaning your playing cards
Using a clean, soft brush like a women’s make-up brush or a softer paint brush tends to work very well. Importantly, it's not a good idea to attempt to clean cards with solvent or water-based cleaners. That being said, using a very small amount of water on a clean cloth to dissolve any sticky substances may work. Drying gently with a dry cloth (and air drying from a distance if possible) is the best way to dry your cards afterwards.