The Federal Government isn't really in a position to do much about housing affordability, as I believe they're restrained by the constitution of Australia; it's essentially the responsibility of the State governments. The Federal government are doing what they can with their first home buyer grants, but it's not helping much. There are a few actions they could take, though, that would send things in the right direction:
While planning is traditionally the responsibility of the local levels of government, in Victoria, the Local Government Act of 1989 says "A local law must not be inconsistent with any Act or regulation"; I would imagine the situation is the same in other states; hence the local government really has very little power over the problem. The only thing I know of that they can do is to ensure that their rates are taxing the undeveloped value of the land, rather than the developed value (and raising their rates to keep the revenue the same). This would have the effect of raising rates on undeveloped land, and lowering it on developed land, which would both decrease housing costs, and encourage those who are sitting on undeveloped land to develop it into housing or some other use.
This is where the problem lies. The various State Governments of Australia are responsible for both the policies that created the problem, and are the only ones able to create the policies that could fix the problem. Each state could begin by making Stamp DutyStamp Duty
Stamp Duty is a state government tax that is charged every time you buy a property. You can read more about it in Land Taxes. a fixed tax (see Land Taxes for details), but the major factor is their town planning policies. As the situation is different in each state, each state needs to be dealt with individually. Click on one of the states below for further information (not all states are yet complete):
What can the rest of us do? There are basically two things: