Not really, no. You're more likely to get struck by lightning than eaten by a shark.
There are certain times of the day you should avoid swimming (dawn and dusk) and certain places too. I used to go fishing with my parents on Fraser Island and there was a good fishing spot where the fishermen used to chuck bait and fish remains (after cleaning them) into the water. This brought sharks into the gutter and then some idiot fisherment would keep on standing around in waist deep water fishing with the sharks nearby. I never heard of anyone being attacked there but it seemed like only a matter of time. But provided you don't do stupid things like that they're not that big a danger.
I find shark nets a bit troubling because other marine life gets caught in them and dies.
Not at all - more than half of shark attacks are caused by instigating them. I normally swim within the boundaries anyway, but if I did spot one, I'd just stay still for a while before it gets bored and wards off.