The first minute matters. Power the phone off immediately — don't wait to see if it still works. Every second the device stays on increases the risk of a short circuit on the motherboard.
Remove any case and SIM tray if you can do so safely. Gently pat the outside dry with a lint-free cloth. Avoid shaking the phone, which can push water further inside.
Do not charge the phone, and resist the urge to put it in rice. Rice doesn't reliably draw moisture from internal components and can leave dust in ports and speakers.
Bring the device to a repair shop as soon as possible. Professional drying, cleaning, and inspection give you the best chance of saving your data and avoiding a costly board replacement.