To remove tarnish: To clean gold jewelry that does not include any soft gemstones, pearls or crystals put the gold jewelry into warm sudsy water containing a few drops of mild dishwashing liquid such as Dawn, Ivory or Simple Green, and rub gently with your fingers or a cotton swab. For more abrasive cleaning (only if needed), brush lightly with a soft baby toothbrush. Be gentle. Even with the added metals, gold is still very soft and easily scratched.
Do not use toothpaste or baking soda to clean gold jewelry. They are much too abrasive. Use only mild non-phosphate dishwashing liquid.
Rinse your gold jewelry thoroughly with warm water and dry with a cotton cloth. Avoid using paper products such as tissues because they contain particles of wood that can scratch the gold's surface.
Before storing, let the gold jewelry lie flat and air dry completely, overnight if possible. Moisture speeds the tarnishing process so it's important to make sure your gold jewelry is dry before putting it away.
Once the jewelry is dry, if it looks dull, rub it gently with a jewelry polishing cloth. Use a clean cloth, or a clean section of a previously used cloth, so that the gold is not scratched. To avoid creating a pattern, rub with the polishing cloth in varying straight lines, not in a circular motion.
Machine cleaning: If your gold jewelry still looks dark, it may need aggressive machine cleaning. Most jewelers have some type of automatic cleaning equipment, such as an ultrasonic, ionic or steam cleaner, and experience using it so they can give you advice about whether such cleaning is safe for your specific piece of gold jewelry. If it is, they can thoroughly clean your gold jewelry for you. The professional ultrasonic machines used in jewelry stores heat the cleaning solution so are more effective than the small ultrasonics sold for home use.
Professional polishing: Clean gold jewelry that still isn't looking like new may be scratched and in need of extensive polishing to be shiny again. This process is done in stages with abrasive papers, not with a polishing cloth, and is a job for your local jeweler. Such polishing will remove some gold so storing your jewelry carefully will save your gold, and save you some money, too.