1. DON'T SWIM IN THE OCEAN
Ninety-nine percent of all shark attacks take place in exceptionally large bodies of water also known as oceans. The way to determine if you are currently in an ocean is to taste the water. If it's salty don't go in.
2. LISTEN OUT FOR THE MUSIC
In the event that you are foolish enough to swim in an ocean, listen carefully for the music, as demonstrated in the marvellous documentary film Jaws. All shark attacks are preceded by the "daah-da, daah-da" chords, which will gradually become more rapid as the shark gets closer. This is due to the Doppler Effect.
3. SWIM WITH FAT PEOPLE
Try to surround yourself with more appetizing companions. If you know them well, you might even try to switch their suntan lotion with Daddies Sauce. This will definitely improve your odds.
4. DON'T GO INTO THE WATER WITHOUT A KNIFE
This is not to defend yourself but to stab the person (aka the decoy) closest to you in the case of a shark attack. Once you are sure the "decoy" is bleeding profusely... swim for your freakin' life.
5. DON'T PANIC
In the event that a shark actually bites you, try to remain calm. This really won't help you survive, but everyone else on the beach will appreciate you not shrieking madly, as this is quite unsettling and can really spoil a wonderful day out. Remember it's not always about you!