Remove all gold plated jewellery when doing pretty much anything that involves heat or moisture...so...bathing, swimming, exercise....and anything else you can think of where the jewellery may get wet which includes by sweating too.
After bathing/showering, wait until you're dry before putting on your gold plated jewels and apply all lotions, makup, makeup fixing sprays and perfumes on before putting the jewellery on. Different chemicals in lotions, makeup fixing spray and perfumes can seriously tarnish jewellery.In general any extra chemical or oils that you apply to your skin are not going to help the longevity of your jewellery.
After every use, clean your plated jewelry with a cotton ball or a very soft cloth to remove any dust and dirt it has acquired.
Store gold plated jewellery in an airtight container and individually wrap each item in plastic bags. Don't chuck it in your jewellery box with everything else as the friction of rubbing up against other metals can wear away at the layer of gold. And leaving it lying around increases the risk of tarnishing.
Don't sleep in your gold plated jewellery for the same friction-y reasons