Sport is seriously the most important and the school already has ~30 A.Mus/L.Mus level musicians. However, academic intelligence is taken into consideration. If you AMC awards, ICAS achievements, etc. they'll all count in your favour.
Volunteering and community work is also taken highly into consideration. Leadership, debating, cadets and public speaking also go down well. If you able to work well with others and lead well, then you should have written proof of it!
Unlike Water recommended, I would highly advise you
not to lie. For example, if you say you are state badminton (although MHS has ~5 per year level) and then don't make it into to Badminton A team (...through trials), then they'll know something is up.
Sports that I would recommend to be good at (ie state level or above): soccer, Australian rules football, waterpolo, athletics , orienteering, swimming, martial arts, fencing, rowing and sailing. The 'Asian' sports like table tennis and bady are already filled with national/state players. Cricket also has state players.
Practice your verbal reasoning and numerical reasoning skills by doing practice questions from the 'basis skills' series books by Peter Howard, and Jim Coroneos. Practice writing analytical and creative essays in less than 15 minutes
These are the same books I used and I recommend them. They are very effective, for example, I got top 11% in everything but verbal reasoning (
).
Remember, you MUST HAVE WRITTEN PROOF OF EVERYTHING! Certificates, printed pictures of medals, etc. If you just talk yourself up for the whole time, then things are not going to go down to well, try and show a bit of modesty. MHS have enough arrongance as it is.