Will you be doing full time or part time?
My tip is to be consistent and get into a work routine. Get used to doing relatively short bursts as well rather than waiting for whole days to be free.
Establish good rapport with supervisors. Get an idea from them early on what they want from you and try to communicate what you want from them in return. Make sure they read and feed back on your work.
Be prepared to feel stupid. PhD study can drain your confidence. Don’t compare yourself to others and remember that what you read in journals and books has been through probably about 10 drafts to make it sound good.
Try to make contact with other PhD students at the uni so that you have a group of people to vent to and who can support you. Expect to feel that nobody else understands what you are going through from the outside world.
Remember that the PhD is not the sum total of your capabilities. You are much more than it and if it is going badly, it’s no reflection on you as a person. You don’t need to write a masterpiece, just enough to pass. It honestly doesn’t have to be your magnum opus.
Finally, expect a huge anti-climax when you finish. You then start to wonder why you stressed about it in the first place.
Do you want a career in academia? If so, think about publication and conference attendance as well as thinking how your PhD can be a springboard to what you want to research when you finish.