Keep up with the news. If you are planning to stay in a foreign country for more than three months, registering with the local Australian post will help it to find you in an emergency. Also let the post know when you're leaving the country. A list of Australian posts can be found here . Ask your travel agent, airline or the embassies of countries you want to visit.
Some countries require visas even for a short transit stop.
Others may turn you back if they find a visa for a country they don't like in your passport. The United States and many European countries have visa-free entry for tourists, but the rules are inflexible and strictly enforced. You might be better off with a visa. A visa is a permit to travel to another country. It goes in your passport.