Visit the Great Southern Railway Web site (see Resources below). Select 'The Overland' train.
Choose which service level you wish to book under the heading 'Compare Service Levels.' There are a few choices with different costs and amenities for each. A single adult ticket is moderately priced.
Purchase your tickets on the 'Bookings' page. Although the Web site is an easy option, the sales office is available as well, within Australia at 13 21 47, or internationally at +011 61 8 8213 4592.
Think about side trips within the journey. The train stops at several small towns with their own fascinations, and if you wish to stay and explore, you can just hop on the next train two or three days later.
Make sure you know where the Melbourne Spencer Street Station is, and arrive one hour before your train is due to depart.
Bring preparations to suit your service level. Red Kangaroo class passengers will need spending money for food and drinks, and a pillow and blanket if you plan to sleep.
Consider bringing binoculars, as you will be traveling through fascinating landscapes with roaming wildlife.