The Law in Australia

Road Rules
Here are some of the rules applied on Australian roads:
In Australia we drive on the left side of the road. A driver must wear a seat belt or get a big fine. If you've been drinking alcohol - don't drive. Arrange for someone else to drive you home or take a taxi. Strict drink/driving laws apply. Get familiar with the speed limits as they are enforced more strictly in Australia than in many countries. Mobile phones are not for use while driving – you can get a fine. Fatigue can cause car accidents and people may get killed. If you feel tired or sleepy, stop your car and take a nap.

Drink / Drug Driving Laws
Under no circumstances should you drive while under the influence of alcohol in Australia. Police conduct random tests along major routes, both in cities and in the country. Drink driving offences are considered serious. Penalties include demerit points, license suspension, hefty fines, and imprisonment.

In Australia, a blood alcohol concentration limit of 0.05% applies in all States and Territories. Special limits may apply to certain driver types, such as learner drivers, public taxi and bus drivers, heavy vehicle and dangerous goods drivers. Random drug testing is also in place in Tasmania.

Tobacco, Drugs and Alcohol Laws

It is illegal to sell, lend, give or supply any tobacco product to, or for the use of, any child. Tobacco can only be sold to a person over 18 years of age. Smoke-free areas were established under the Public Health Act 1997. It is not permitted to smoke in all indoor public places. This includes offices, shopping centres, factories, hospitals, bars, gaming areas, restaurants, corridors, toilets, function rooms and movie theatres.

There are penalties for people who smoke in smoke free areas.
Smoke-free vehicle law - bans smoking in vehicles carrying children under the age of 18. A $120 infringement notice can be issued on the spot for the offence.

Drugs
It is illegal to posses, sell, grow or import cannabis (marijuana). This also applies to amphetamine, heroin, ecstasy, cocaine and opium poppies

Alcohol
It is illegal to supply alcohol to those under 18 years of age.
It is illegal to drink or posses an open container of alcohol in a public street. This does not stop you enjoying a picnic in a park or partying on a beach where council by-laws permit. This law is aimed at anti-social behaviour that impinges on the rights of other members of the community.

Source: http://www.police.tas.gov.au/security_and_safety/information_for_visitors