Step 1: Do NOT turn on the phone
Step 2: Pull out the battery and SIM card
Step 3: Rinse quickly in freshwater if you dropped your phone in salt water (to rinse out the salt)
Step 4: Dry your phone using compressed air (DO NOT dry it in the oven)
Step 5: Cover your phone with uncooked rice (in a ziplock bag) for at least 24 hours (to absorb moisture)
Step 6: Turn your phone back on and see if it works!