Stick it in silica (not rice)
You've probably heard that the next step is to let your phone sit in uncooked rice for a few hours. That's fine if it's all you have on hand, but it isn't ideal. The rice can absorb the water, but not as efficiently as you think, and you don't want the grains winding up inside the phone itself.
A much more effective option is to drop it in a sealed container with those silica gel packets you sometimes find when you buy new clothes. Start collecting them now, keep them in a container with an air-tight seal (so the water they absorb is from your phone, not the air), and drop your phone in there, along with the SIM car and battery, for your best shot at saving it.
Now, if you're out and about and decided not to carry any rice or silica gel packets with you, that's fairly understandable. Instead you may want to invest in a Bheestie product -- little bags designed specifically for saving your electronics in these moments of crisis. Have one on hand, drop your phone in, and hope for the best.