Mosquitoes are not only an annoying pest to you, your family and pets, they are also transmitters of pathogens and parasites. Some of the common diseases known to be caused by mosquitoes are Filariasis (Heart Worm), Epidemic polyarthritis (Ross River Fever), Australian encephalitis (Murray Valley Fever).
Breeding occurs in any stagnant water body so make sure your property does not have water lying around. In order to prevent breeding you should change water weekly in bird baths, stock ponds with fish, make sure your roof gutters drain properly, remove pot plant saucers or fill them with sand, check funnels of bromeliad plants, screen or cover septic and water holding tanks, and keep lawns and other ground vegetation short. Partly emptied swimming pools containing dirty water are very likely to breed so demolish your pool, fill it in or drain it completely if not used. But now they're back and breeding, possibly in your own back yard and this makes YOU a target for their next bloodmeal. You could also be exposed to viral and parasitic attack.
For more information on Mosquitoes see NSW Dept. of Health.