Spending next summer in australia. need help?

Question

Next summer I'm going to Australia by myself. i'll be 17. i have people to stay with but i'm going to be in the Sydney and Melbourne areas, touring uni's. I was looking for tips like best transportation and how to not p**s off locals. i cant rent a car because i'm not 25. Also whats the best way to get from melbourne to sydney, something thats not way overpriced either.