What habits should I build in the first part of my PhD?
To get the ball rolling, I will offer an answer.  I will invite others to edit my answer to improve it, or write another answer.


In the early part, spend about 5 - 10% of your time looking at journal articles and other scientific literature (if you are on top of your coursework).
Form one or more study groups, if for no other reason than to get practice communicating about your subject area.
Attend seminars.
Visit office hours.
Try to keep your notes organized.
If there are foundational exams in your program, get some old exams and start looking at them, as time permits.
Find fun ways of getting exercise.