AFL rules!
Work the legs, lots of running. Do leg presses which help for sprints, but do distance running as well. Need the legs for kicking too, can't score a goal without a good leg. Work the calves too, do squats, lunges, and the leg curls (work calves and hamstrings).
Be sure to have an medium strength upper body, not as important though, only for tackling and breaking tackles. Don't need throwing power since you punch it.
Have fun, I wish I played that, but they don't have it in America. I watch it on TV though
