GetUp have created a rather nifty little website called HowShouldIVote.com.au, which allows you to fill in a quick quiz to establish roughly how you should fill out your preferential vote card for the House of Representatives. (Such an exercise for the Senate would require SETI to power, which is why they don't offer it.) It's not 100% foolproof - my results had the CEC ahead of the Greens and the Liberals ahead of Family First - but it's near enough, and if you aren't too fussed about how the numbers after 3 flow, you may find it useful. (I wouldn't be devastated if my vote was submitted the way GetUp generated it, I just want to switch a couple of minor parties around.)
If the whole preferential voting thing makes your head whirl, GetUp have thoughtfully provided a mostly non-partisan guide to the Australian electoral system in plain English.