There is a very useful thread up at Feminist Philosophers on the unwritten rules of the game of being a professional philosopher, as they apply to publishing, collegiality, teaching etc. A lot of knowledge we acquire as academics is tacit, not systematically taught or collected, and we have to discover it piecemeal over time. Some supervisors and programs help to make some of the tacit knowledge explicit (e.g., by organizing workshops on how to put together a good job application), but many do not. In any case, even if we take that into account, I think most knowledge transmission about academia is still informal.
Yet such knowledge is vital to thrive as an academic. Is it OK for a grad student to approach a specialist in her field she have never met before to ask for feedback on her unpublished paper? Is it acceptable to use someone else's syllabus as a basis for your own course? When is it appropriate to contact a journal editor to gently remind them about your paper? On the thread is a lot of useful knowing-how information, but next to that there is also a lot of tacit knowing-that information that more experienced academics have.
For instance, as an undergrad I did not appreciate the difference between professors and various forms of adjunct faculty and postdocs. I simply saw them all as professors, cozily tenured until retirement. And this is a common mistake: an author for the Chronicle of Higher Education recounts how students at a liberal arts college thought her title 'visiting assistant professor' meant she was a distinguished tenured philosopher, visiting from another faculty. They assumed after her contract ended she would safely return to her home institution. The bleakness of the job market often only becomes apparent to people in their final years of graduate school.
We learn to avoid these confusions as we get more acquainted with the academic milieu, but the fact that I'm still learning suggests to me that it is a long process. How do we gain tacit knowledge? Home milieu plays an important role. One of the commentors at FP remarks "I'm the first Ph.D. in my family, so I had a lot to learn about the culture of higher ed." I think this may explain (although I have no numbers to back it up) why so many academics have academic parents, and perhaps even - with the increasing tightening of the job market - why children of academic parents may have an advantage on the job market.
Personal contacts with supervisors and other academics (e.g., at conferences, over dinner with faculty members) is also very important. Again, this is a source of inequality: people from smaller programs have smaller budgets for travel and can therefore not enjoy the informal contacts of conferences, people with caring responsibilities may not attend informal gathering of faculty members frequently. To give a stark example: suppose you are at a conference where there is a conference dinner, held at a fancy location, with a fixed price of $50 (not uncommon). Poorer people will tend to skip those dinners, thereby missing vital opportunities for informal mentoring and networking.
One way to combat this inequality is to put more effort into mentoring and other programs explicitly aimed at transmitting tacit knowledge about academia. Ideally, this should already happen for graduate students. But it should be a sustained effort. Indeed, given the importance of tacit knowledge, supervisors should not constrain useful remarks about such things to informal situations, but actively incorporate them also when they meet the student to discuss his or her work - e.g., suggesting possible venues for publication for an unpublished piece. Again, some supervisors do this, but I also know many who do not. It also seems useful for a grad student or early career scholar to have a mentor to discuss the nuts and bolts of academic life who is not the supervisor. The SWIP mentoring scheme is a useful initiative.