In order to maintain the condition of your coins, you should certainly take proper care of them. As you know, gold coins don't rust, tarnish, or corrode--a great advantage to owning the metal. Silver does tarnish, and both metals can get dirty and worn down. Thus, handling uncirculated coins should be limited. Your fingers leave prints, dirt, and damage the intricacies of the design if handled too often. Experts suggest using white gloves, or holding the coin on its outer edge.
Graded, uncirculated coins are usually placed in a special case with a seal displaying the grading company. These cases ensure that the coins stay clean and free from damage. If your coin is not encased, then go to a local coin dealer to purchase coin cases with lip covers made of a special protecting plastic.
Store coins in a cool, dry, and safe place. No one can tell you what place is most safe for you. You must choose an accessible place where you'd feel most comfortable leaving them for long periods of time. Experts often recommend using a bolted down safe in your home or a bank safety deposit box. Alternatively, you could opt for a storage program like Goldline International which enables you to buy and store coins or ship yours to their storage facilities in Santa Monica, CA. The most attractive reason for such an account is liquidity. Besides, it's America's oldest bullion storage program with about 60 years of experience.
On the East Coast, the Delaware Depository offers an exchange-approved storage facility (meeting the storage standards of commodities exchanges like NYMEX, COMEX, and CBOT). It's proximity to major cities and its location in the Wilmington financial district, make it an attractive option.
There are many other bullion storage programs mainly located in New York City, London, and Zurich, but there are far too many to list. Whatever choice you take, make sure you do take care of your coins, research, and use your best judgment before storing.