Wear dog tags. There are no sure ways to survive tsunami's (Although being an expert on 'not drowning' can help you if you are not knocked unconsiousness by the wave itself or something else), but ensuring that people know who you are will help the relief people a lot. A forensics expert showed me pictures of his ID work in Sri Lanka, and those pictures where gruesome. Quite a few people working there eventually couldn't take it anymore.
Oh, in case... Try not to swim too much. Floating is better. Swimming during a storm or other circumstances where a lot of current is involved is bassicly fruitless and gets you nowhere, only leaves you exhausted, after which you will probably drown.
