I am Australian and my Hubby and Kids were born in the UK. although we have been together for almost 20 years, he needed a spouse visa. i think you need to prove you have been together for 2 years or more, you need to say how you met, get people you know that are australian to write to say you have been togfether, have photo's to prove it as well.
we applied whilst in australia as i had a dealine to start my new job here when I moved from the UK. as soon as you apply, they put you on a bridging visa. whilst on this you cannot work or leave the country. within a few months, if there are no issues and you have completed the forms the permanent visa is granted.
I completed all forms myself without the use of an agent and i had no issues. it was very easy
Hope this helps