(Excluding the overage players drafted from State Leagues)
You must play at least one game with a WAFL / SANFL club at some level (including Colts).
Playing for one of the elite schools is a big help. Teams like Hale and Sacred Heart will have a draftee most years.
This year only one WA player (van Berlo) and 3 SA players (Hartlett, Tiller and Slatterly) were taken after being overlooked in last years draft. All the others were first run talent. 3 of those guys have represented their state at under-18s so you have to get to that level.
The only 2 guys from WA-SA taken did not play at Under-18 Championship level were Rusling and Tiller. So you want to represent your state.
Anywhere between 15 and 20 of the kids taken (more than a third) will have made the elite AFL-AIS academy. This year - Roughead, Deledio, Gibson, Garner, Stribling, Monfries, Deluca, Wood, Franklin, Maric, Williams, Wells, Copping, Griffin, McQualter, Sherman, Morton and Tambling.
So, with a few exceptions, you'd want to play under-16s and under-18s for your state, making the ALF-AIS squad is a big help, and you pretty much have to get invited to draft camp.
Even if you can manage all that you'd better be able to kick, and have to be quick and mobile. Every year the kids seem to get more athletic and almost every year new records are set at the draft camp.