Turn off the water supply and flush to lower the water level
Pour white vinegar into the bowl and let it sit
Sprinkle baking soda into the stained areas
Scrub with a toilet brush
Use a pumice stone on stubborn mineral stains
Apply a toilet bowl cleaner and let it sit as directed
Scrub again and flush
Repeat if needed
Wear gloves while cleaning
Avoid mixing bleach with vinegar or other cleaners