The subject of cleaning jewelry, in my opinion, is full of just that - lots of opinions and experiences mostly dependant on the composition of the piece.
Before, I go into what I've found for cleaning jewelry, I would like to offer two suggestions to prevent the necessity for cleaning.
1) For most pieces, using common sense is one of the best suggestions. Keep jewelry away from perfumes, dirt, and sticky things. Make sense? Keep the piece as clean possible and keep chemicals away.
2) When not wearing your pieces, protect them. Silver can be kept in zip lock bags (to keep the air away) or in silver protective, soft cloth bags. Other pieces should be stored in dust free places. Make sense? Protect them from the elements.
OK, now your favorite piece is dirty. What to do?
As a first step, usually items can be washed in gentle soap, rinsed and dried. I often wear my silver chain maille bracelets in the shower. Because I wear them all the time, they tend to get just everyday dirty - like me. A shower works wonders.
If you have copper in your piece, rub with a mixture of lemon juice and salt. Lots of salt. The new penny look will come right back. It is suggested that you then rinse in a mixture of baking soda and water. This stops the chemical reaction and avoids any possible pitting. I usually follow this treatment with tumbling which adds shine.
Then there are the dips and sonic cleaners and shining cloths. Leather is an entirely different ball of wax. Silver plate, gold plate and some other metals just wear out (in my opinion) and there isn't much you can do to make them brighter again. Ribbons might need to be replaced.
When I started this post, I forgot how many, many ways there are to clean jewelry. However, my first two points, I think are the most important. Treat your jewelry well. Then, call Bev if you need more ideas or suggestions.