It's never too late or too early to think about call maintenance.  Below are a few tips you may want to consider.

Slate Call Maintenance
Pot and peg calls, also known as slate calls because of the primary material they were once made of, now come in a variety of surfaces. Whether your call is made of glass, aluminum, slate or some other material, using some general maintenance rules can make them last for many hunting seasons.
Most importantly, always make sure to keep fingers, other oil surfaces and dust off the striking surface. Use storage pouches, holsters or plastic bags when you are carrying your slate calls or storing them. Store your calls in a cool, dry place to prevent the warping of the call's wooden chambers.
Keep your call surfaces sanded, and only sand in one direction. Never sand back and forth and certainly not in a circular motion. Sanding in one direction makes for a more reliable sounding sweet spot from which to pull your best calls.
Use sandpaper, light steel wool or a sanding stone to rough up the surface of the call. A good rule of thumb is to use light grit sandpaper for true slate calls and heavier grit for other surfaces.
It's also important to lightly sand your striker tips with an emery on a regular basis to clean them of oil and dirt. Like your calls, sand the striker tips in one direction as well.

Box Call Maintenance
A good box call is one of the most costly calls to buy, but proper care in the field and regular maintenance will turn that crafted piece of wood into a loyal companion in the turkey woods for many years.
When maintaining your call, the first thing to remember is to keep the call's surfaces clean and do not ever use sandpaper on it. Sandpaper can change the tone of your call.
It's also important to handle your box call carefully. Keep your fingers off the striking surfaces: the edges of the box and the underside of the lid. Skin contains natural oils, which can affect the sound and life of your call. Make sure to use only chalks, such as box call, teacher's or carpenter's chalk. Stay away from chalks with an oil or sugar base.
Only use chalk on the underside of the lid. The beveled edges of the call are important in its design, and use of chalk on the edges can wear them down.
Make sure you blow out the sound chamber of your box call from time to time. This will get rid of any chalk dust that might have settled.
Storing your box call is simple. If you don't have a holster, store your box call in a large, plastic bag. This will keep moisture from getting to the call.
By following these simple tips, your box call may become a collector's item some day.

Mouth Call Maintenance
One way to get a jump on next year is to make sure you keep your calls in good working order. This is particularly true of your mouth calls, which can dry out if not properly stored.
Mouth call care should begin as soon as the call comes out of the package. It should be washed with warm water to remove any latex residue. Then, if you like, spray it with an antiseptic mouthwash.
After use, put your mouth call in a case or a plastic bag and place it in the refrigerator. This will provide a dark, cool environment, and the colder temperature will tighten the latex reeds, which will provide optimum sound.
A flat toothpick is also helpful in mouth call care before and during storage. Run the toothpick between the reeds to clean them, always being careful not to tear the latex. When storing, place a toothpick between the reeds, so they won't stick together between uses.
A word of caution: store your mouth calls away from heat sources. Heat will cause the latex to expand, lose pliability and create too much vibration when used.