Instructions
Power down the controller immediately by holding down the home button and selecting "Turn Off Controller," if possible. If the controller is charging by USB, unplug it.
Wipe down the front and back of the controller of excess water or liquid. Either place the controller face down over a towel or into a plastic bag full of uncooked rice.
Wait at least 24 hours before attempting to use the controller again. Some prefer to use the uncooked rice because moisture is actively drawn away from the electronic components, just like a silica packet inside of certain manufactured goods.