The gold plating used for guitar hardware is similar to gold plating used on lower-end jewellery. Over time, this gold plating will oxidise and even start to develop a greenish tint due to the oils and sweat that get onto the gold metal parts when playing. It's inevitable that gold hardware will need to be cleaned because if the guitar is played, the gold will start to lose lustre and will oxidise.
Remove all of the gold hardware from the guitar. In general, all hardware can be removed using screwdrivers and small boxed-end wrenches. Electronics do not have to be removed, but if your guitar is equipped with metal-covered pickups, you will need to de-solder the covers from the bottom of the pickup with a de-soldering iron or a soldering iron with a de-solder bulb.
Clean the hardware in warm water with a mild dish soap. Use your fingers or cotton towel to clean the hardware. Do not use any abrasives such as scratch pads as these will scratch and dull the finish. All oils, dirt and residue should be removed while cleaning. Wipe the hardware clean with a cotton towel.
Polish the gold hardware with a precious metal rubbing compound and a cotton towel. This will remove oxidation and micro scratches that have dulled the finish. Polishing compound can be found at most jewellery retailers. Aggressive polishes should not be used as there is a risk of polishing through the gold plating.
Replace the hardware in the same manner that you removed it. To reattach the pickup covers, the covers must be soldered back into place.
Preventive maintenance is key to preventing the need for a full tear-down and polish of all the hardware. Wiping down the hardware after each use with a clean cotton towel will help limit oxidation. Also, many people spray their gold hardware with a polyurethane hard coat to prevent oxidation.