I've been doing it a bit with ds... am going to try and be more consistent now. He's 10 months old and I have chosen bottle, drink (for water to differentiate from formula), eat, book, sleep, mummy and daddy. They say you should only use a few signs at first.

If you don't want to buy a book there is a free AUSLAN signbank website that you can look up any signs you want. That way you can just choose a few to get started with: auslan.org.au

I've also bought a wall chart from everybabysigns.com.au which has selected signs for babies and young children but is still AUSLAN based.