First, retrieve it as quickly as possible. If your phone is still in the bottom of the jacuzzi or the toilet, get it out ASAP. The longer it’s in the liquid, the greater the likelihood damage will be.
Once the device is no longer submerged, if you can, take that battery out. Don’t even bother powering it off, don’t press any other buttons, just open up the phone and pull the battery out. If you can’t do that though – if you own an iPhone or another device that’s impossible to quickly pry apart – you’ll have to settle for just carefully powering the device off. You want to cut off power in the device as quickly as possible to prevent the possibility of a short circuit.
Now – Do not blow-dry it or stick it in the oven. The heat can damage the delicate electronics inside. What you should do is give it a quick wipe with a clean towel, making sure no water accidentally ends up draining into its ports or other openings. If there are traces of water trapped inside cracks or indentations in the case, try carefully and conservatively using compressed air to blow it out. Just be careful not to blow the water further inside the phone.
Next we have a few different options. Many folks swear by stuffing your phone in a bag of dry rice, and letting it sit for 24 to 36 hours or more. This is cheap, easy, and can be done in a pinch. But this method could have some negatives: If the rice absorbs the water well, you may be left with a mushy rice mess stuck in its creases and I/O ports. Those with skin in the game (as you’ll see below) also say that the starch from the surface of the rice can get inside your phone and muck it up, but I haven’t been able to find solid empirical evidence of this. To be safe, wrap the phone loosely in a paper towel before dropping it into the rice.
The smartest option is to keep synthetic desiccants on-hand. They are far less messy, and they work more quickly and efficiently than rice.