Use sun protection as the sun is quite strong (sunscreen, sunglasses, T-shirt, hat etc.)
Swim in between the red and yellow flags at the beach (these are the safest water conditions and is where lifeguards will be).
If you get bitten by something, do not touch the wound, try to take a photo of what you got bitten by so that the poison can be identified.
If you decide to travel around Australia or go hiking, bring a first aid kit with pressure bandages and plenty of water.