Simple, fast, and all you need is salt and vinegar. A mild abrasive (like baking soda) helps remove physical dirt and grime. A little hand or dish soap is optional.
Remember, NEVER clean an item of value unless you’re confident you know what you’re doing. Cleaning coins almost always ensures they’ll be unwanted by a collector, essentially reducing their value to whichever is greater; their junk value, or their face value.
The process works on copper as well as on its alloys. I recommend it for brass, bronze, and other alloys with 80% or greater copper content.
I also have a video on removing tarnish from silver coins: http://www.youtube.com/watch?v=Kp62AvR7kFM
If you have comments, questions, or suggestions: please leave them below!