on a serious note to be a police officer you need to be physically fit so id start working on that now if you're not already fit and it would probably be beneficial if you did some form of defensive martial arts.
It's recommended that you have a BMI of less than 30 (unless its obviously pure muscle) and you need to at least be on your green p's.
I'd also approach the local police station and ask them for a recruitment package, if they dont have one on them they'll be more than happy to send away for a package.
Visit here for most of the recruitment stuff
Recruitment & Education - NSW Police Force