1. Resist the urge to clean the coin. Cleaning will ruin the condition of the coin, introducing scratches and blemishes, and removing patina. If you’ve dug the coin up and it’s so caked in dirt that you can’t see features or dates, put it in a safe place until you get home. Never try to brush or rub dirt off in the field. Some experts allow for careful soaking of dirt-caked coins in oil or distilled water to remove the dirt, while others opt for professional cleaning. If you do soak, let the dirt slough off naturally after soaking; rubbing it can introduce scratches to the surface of the coin. Allow the coins to air dry, or carefully pat them dry with a soft cloth; do not rub them.
2. Always hold the coin by the edges, never the face. Consider using lintless cotton gloves (never latex) or a soft cloth to handle the coin. Get it into proper storage as soon as possible.
3. Store it properly. There are lots of methods for storing coins, but some are better than others. Even if you don’t yet know if the coin is valuable, you can save yourself the headache of worrying by getting decent protection for your coin. The first rule is always to use supplies specifically designed for coins. Many non-coin items have chemical or other properties that can severely affect the value of a coin; items made for coin-collecting will be formulated to avoid this. Do not store your coins in or around anything containing PVC, as PVC has a very negative effect on coins. You can use plastic or paper coin flips for a short time, but they are not airtight, so it’s recommended not to store in plastic for more than a few months. Cardboard holders with Mylar windows are another solution. If you choose this method, make sure to staple the holders very carefully, being sure not to get the staples too close to the coin. It’s best to use stainless steel staples, to avoid the danger of rust.
Hard plastic holders for individual coins, referred to as “slabs,” may be a little pricier, but they often offer the best protection for the cost. The best coin protection is a hard case known as a slab, but this can be an expensive process, so it may be best to wait and get the value of the coin before spending the money to have it slabbed. Never store any coin in aluminum foil: moisture in the air can react with the cheap metal and cause corrosion, damaging a coin beyond repair.
4. Get a guide. There are many books on identifying coins, such as the Official Red Book; you can also search Google and Wikipedia to find other coins that might look like yours.
5. Consult experts. Go to a local coin shop if you have one. Join coin forums like CoinTalk, Coin People, or NumisSociety, and get the input of fellow collectors. Check to see if a coin show is happening near to you any time soon.