Know the rules of your PhD program!

Make sure you become well-versed in departmental, college, and university rules applicable to doctoral students. Don't waste your time at a PhD student orientation daydreaming about the scientific discoveries you will make (you will make none) or trying to meet other PhD students (they will not become your friends anyway). Listen to the rules and policies instead. Create a folder where you keep all the handbooks. Make sure you take some time to go through those handbooks. You don't wanna be caught off guard with an accusation that you have violated a rule.

Professors usually don't know those rules themselves. They have their own problems and knowing PhD program rules is the least important (or non-existent) thing on their priority list. Their legal nihilism is often replaced with legal fundamentalism when they want to find a formal reason to kick you out of the program. So don't put yourself in a vulnerable situation because of your own ignorance.

Just to give you an example. We had a lot of doctoral seminar classes where we would usually get "incompletes" instead of a grade at the end of a semester. This had to do with the fact that faculty always wanted a publishable paper as an outcome of every doctoral seminar course. They marketed this requirement as rigorous training. However, it was more due to them wanting to get papers out of us. Well, as you know, writing a publishable paper in a new area may take you much longer than one semester. Moreover, after the class is over, your prof may be too busy to get back to you and grade your paper. As a result of that, many doctoral students in our program would have several incompletes after 2 years in the program. There's a rule that after certain amount of time an incomplete becomes an "F". There's also a rule that that a PhD student who gets three grades of C- and below is automatically dropped from the program. So quite a few students would find themselves with 1-2-3 Fs on their transcripts. Which is not really their fault yet a violation of PhD program rules.

We had a guy who was an exceptional doctoral student. He was very hard-working. Had a few papers already published. Did excellent job teaching. However, he was too independent (didn't kiss up to people much) and some faculty members did not like him. So his "bad grades" (mostly due to incompletes) gave them a perfectly legal reason to drop him out. There was nothing he could do. He violated the rules.

Of course, this is a rather extreme case and this probably doesn't happen too often in PhD programs. Still, keep those things in mind. Do not make yourself vulnerable. You can recover from the outcast state only if you are not terminated from the program.