You don't need to do anything out of the ordinary to post internationally, and it's really not much different from selling locally, although I recommend that you acquire a decent digital scale first.

The following downloadable PDF file from Australia Post will tell you all that you need to know, including all the prices and rates for different weights and postage methods.

http://auspost.com.au/media/documents/international-post-easy-guide-ms160-31mar2014.pdf