The ATO has some very helpful information regarding invoicing. Their web site  contains extensive resources for business start-ups.

One useful booklet, downloadable as a PDF file, is “How to set out tax invoices and invoices” which provides voluntary standards for invoices and tax invoices. In only six pages, just about everything you want to know about how to produce an invoice is covered with examples and explanations.

If the link above isn’t working, go the the ATO Business page and use the Search facility at the top right of the screen to find NAT11675.