First and foremost, turn it off, do not turn it on!

Second, take the battery out.

Third, shake and blow dry.

Fourth, put it in something to dry it out.  Suggested methods include wrapping it in a towel, then into cat litter.  Or directly into a bag of rice or silica beads.

Fifth, wait.  At least two days.

Sixth, put it all back together and hope for the best!

Note: more helpful tips via the above links.