Pre-treated cloths or expensive cleaners are not required (the use of pre-treated jewelry cloths on electroplated pieces will wear down the finish at an accelerated rate).
Another thing that helps to preserve the high-quality finish is to make the jewelry the last item you put on, and the first thing you take off when you get home. No perfume, lotion, sunscreen, etc. In addition to storing the jewels in a dry place, this will all work to minimize exposure to liquids and keep your gems in great shape.
It is very important that abrasive jewelry cleaners are NOT used on plated items -- that applies to all plated items, no matter where you get them. As an example, the cloth used to clean sterling silver has an embedded mild abrasive in it, and it will remove and score (or abrade) all plated products.
PLEASE DO NOT USE JEWELRY POLISHING CLOTHS ON ELECTROPLATED ITEMS.
The best way to clean the metal on plated jewelry is with a simple cleaner (like Mr. Clean) or mild liquid soap and dry with a cloth. Be careful not to use cleaners on your stones or crystals. They should be cleaned with a dry cloth only.