I would start with some of the more well known locations; just until you're comfortable, and try to keep track of anything you see that looks like it may be interesting (in terms of new locations).
If you get told to leave (or meet anyone especially unfriendly), be polite, move on quickly. Try to leave the location as you find it. A quick google should give you some... acceptable locations for your first couple trips, and with some digging you can find some better locations, although a lot of locations that you find online will be shut down/locked up, and some of them may have cameras.
If draining, check. the. weather. Make sure there's no rain coming, flash floods are common. A waterproof bag is expensive, but handy, a flashlight is a good idea, two flashlights are a better one. If using your phone for light, bring a portable charger.
A set of spare clothes is useful, good shoes are needed.
If you don't mind me asking, whereabouts in melbourne are you?
(pm me if you want anything, too)
young, eager, and not completely inexperienced