Cleaning Coins - Dont Do It
One of the first rules of coin cleaning is "Don't clean your coins." Well I guess there is some clarification needed here.
Over time, coins naturally undergo a process known as toning, when oxygen or sulphur reacts with the metal. While it may not look pretty, the surface under the toning still contains the reflective quality known as mint lustre. You should not do anything to a coin that you think will improve the coin. In other words do not shine it up using Brasso or Silvo. Do not use coke or lemon juice. Do not use vinegar. Do not use toothpaste and toothbrush....the list goes on. All these are acidic or abrasive and will ruin your coins. You should not use anything that will shine up your coins as this will remove the natural lustre or toning off the coin. This will also decrease the value of the coin.
However coins will often have on them built up dirt and grease. This may get into the nooks and crannies of the coin. To remove this type of build up you can use a weak detergent solution with a soft cloth (Clux Wipe or similar will do the trick) to take this material off. There is also nothing wrong with using a cotton bud or toothpick to gently get into those hard to get at places. Avoid soaking your coins as the detergent can react with the coin.
As a general rule if you are unsure, do not do it, bring your coin in for advice. If it does not come off with soapy water and a soft cloth, bring your coin in for advice.