So, what to do if you drop your phone in water in order to give a water damaged device the best chances of survival... or at the very least the greatest hope for successful data recovery?
Remove the device from the water, and if possible, turn it off! Water and electricity don't mix. Do your best to fight the urge to turn it on or plug it in "just to see". This simple act can turn a repairable phone into a data recovery job very quickly!
There is the ridiculous rice myth, which is nothing more than a placebo. It gives people the impression that they are doing something which will benefit the phone, but it's no better than just leaving the phone around to air dry naturally. Rice can't do anything to remove the corrosion which often happens almost instantaneously as seen in this picture:
Ideally the phone needs to be opened up (best while still wet where possible), and all the liquid needs to be displaced. Also along with the liquid, all the trace elements such as salts and chlorides and the corrosion need to be removed from the board. This is best achieved through an ultrasonic cleaning process.
Once the board is cleaned, then it's necessary to touch up all the areas of damage in order to remove any oxidization which has formed in the solder joints. Also, any bad components need to replaced, and short circuits rectified.
In essence, it's largley about time. the quicker you get it opened up and put through this process, the chances of success are far greater.