Like this please:
Suite 1, 234 Main Street (or, say, PO Box 1234)
Suburb, NSW 2999
Australia
If you have multiple offices please give each office a title, eg:
Sydney
Suite 1, 234 Main Street (or, say, PO Box 1234)
Sydney, NSW 2000
Australia
Melbourne
Suite 1, 234 Main Street (or, say, PO Box 1234)
Melbourne, VIC 3000
Australia