The ACER website should have everything you need to know. Other things I learned in my own process, or later on are:
(Applies to grad entry):
1. You can apply to 3 graduate entry schools --- USyd and Flinders U have their own application forms and you can apply directly to them. You can use ACER for a third school that doesn't have their own application.
2. You need to take the MCAT (ACER will let you know that). General guidance is aim for a 30O. That gives you a very good chance. Many do get in with a 27-29, and some even lower, I believe. Not sure how important the essay portion is... but an "O" is what is recommended for US schools, and specifically quoted to me by my Uni.
3. ACER tells you how many intl students are accepted in each school. Choose wisely. It was 40 for USyd, 30 for Flinders last year. 10 for ANU, 15(?) for UMelbourne.
4. Go to the school websites for more information, or do a google search (especially if you do not have their website address). Some have picture tours and video snippets of their school. Good to take a quick glimpse prior to deciding/applying! You can also try emailing some of them for the information you need (I did... and got immediate response and courteous/helpful advice). But note that not all schools are as nimble... searching past forum posts will tell you that USyd has a poor record for response. They were severely underfunded and understaffed.
5. Many schools with grad-entry are PBL based, make sure you know what it is (google search and read up). See if you like it, and prepare for it in your interview.
6. Many schools would be happy to let you sit in some of their tutes/lectures. Pitman might be the most experienced in this in the forum... I didn't do anything like that. But if you can fly to Australia and take a look first... that's nice.
7. Yeh, get some general knowledge of Australia. Like it is below the equator, and the world is topsy-turvy. Just kidding. But yeh, the seasons are 6 months off, so Feb is their Fall... we all start the year in Fall that means (US and Australia at least).
8. Check the forum for all the information on returning to US for FMGs and USIMGs (especially for you), unless you intend to practice elsewhere in the world!
Actually, there isn't that much to know even if making a list makes it seem complex and you'll learn more on the way anyway!
Good luck!