What would a PhD graduate advise a new PhD student?
Remember there is a 90% chance that your adviser won't give an F*** about you, they may even sabotage your work and withhold information or give you false info. Academia is a cutthroat operation and professional academicians like your adviser only care about saving their own skins because they don't really have the skills to survive outside of academia. So be prepared, these people are not being paid to teach and mentor students like undergraduate professors were, their job survival is based on only two things, churning out papers and writing grants. My advice is to spend the minimum amount of time on any dead end project your adviser asks you to do and avoid donkey work, DON'T waste time with any college busywork, seminars, guest speakers, going to courses or meetings unless its absolutely required. DO take full advantage of your student access to the University Library and its journal subscriptions and specialized texts in your subject, these are your teachers and mentors and access to these materials are the main advantage of being a PhD student at a University. Decide on your project early, stop fantasizing about it and go to the journals to outline how you are practically going to do it and learn what worked and didn't work for other people working on the same idea, and yes if you dig enough in the literature you will always always find someone who has published on your idea or close to it, and if you don't, it just means you haven't looked hard enough.
Main Points would be to get maximum use out of all of the University resources available to you as a student, minimize time spent on jumping through academic hoops, bureaucratic BS and any donkeywork your adviser gives you as much as possible and the most important thing is have your own project that is conceived and carried out by you and spend the maximum amount of time on this and getting it to produce results, tell your adviser and anyone else you don't trust the minimum you have to tell about it, draw on any colleagues, resources and mentors you had before the PhD, to get things you need done and don't ask anyone if you can do something you need to do, just do it, if you ask, they will say no.
The main thing the PhD teaches you is how to act independently, drive your own project and get results in a hostile environment. No one is going to do anything for you or hold your hand, in fact academicians and higher-ups will pull you down and sabotage you if you give them a chance by acting like the cute trusting undergraduate student that you used to be. As a PhD student you are almost at their level and professors are beginning to see you as a threat and as the competition, so keep your own counsel until you get some project results that they can't touch.