Waiting until the class for general announcements would be the norm. Office hours and the telephone were always available for students if they had a question, and a last minute cancellation would be announced, as often as not, by a notice posted on the classroom door. Truly urgent information could be passed by phone tree, if one had been set up, but generally you came early, stayed late, or used office hours to clarify any of the dozen little questions that these days might be sent in an email. Most emails I see about classes these days are matters of convenience, not urgence, and waiting until the next class wouldn't really be a burden.

I'm not sure there is a way to cite this properly, especially without violating the 20 year rule. I think it's probably a sufficiently Meta question though that this answer should be acceptable.

I was an undergrad in the mid-'90s, so email was just hitting college campuses, but professors weren't yet using it for class purposes (I don't think I ever had an email exchange with a professor).

It was pretty simple: everything you need is in the syllabus, and anything not in the syllabus gets announced in class. That was it. If students had questions, they went to office hours.

I'm a prof now, and I can tell you some faculty procrastinate because they know they can just send out email announcements. I've probably done it a couple times myself. In the past, you planned everything ahead of time because you knew you had to give information out in class, but now, it's easier to put it off because you know you have email as a backup. Having assignments ready before class used to be a top priority, but now, if there's some other pressing matter I need to attend to, I can just say "I'll email it to you by the end of the day". And students do the same thing: in the past, students would get to work on assignments earlier because they knew that if they had questions, they had to get to office hours on Tuesday; now, they can send last-minute emails to professors (and get angry when we don't write back 30 minutes later).

As for class cancellations: you used to have to show up to class to find a note on the door. That's one thing I really appreciate -- being able to notify students about cancelled classes, because I do feel really bad for the people who had to drive to campus for no reason.

Required readings for the first class, if any, would be posted on a departmental bulletin board. Exam results were also posted in such corridors, by last name for many decades, but with new attention given in the 1970s to student privacy, posted by student ID (which was generally Social Security number).

Any communication from the professor to the students was either spoken by the professor in class, or was posted on either the classroom door, the professor's office door, or in the case of the music school I went to, on the bulletin board in the hallway of the conservatory. It was the students' responsibility to check these places regularly, and students would often pass the word along that there were new announcements posted. For instance, test results would often be posted on the professor's door, with the students' social security numbers substituting for their names. We didn't worry much about ID theft back then (late 70s/ early 80s)

Since my college days were in the 60s, I guess that meets the 20-year rule. As was said, basically a notice on the door was all you got. One of the unwritten rules was if the prof didn't show up to class after 10 minutes of waiting, we passed around an attendance sheet that after we all signed, someone would take to the department office, and then we were free to leave. I don't remember there being any phone trees set up, but we were a very large department (some of the smaller majors could have had phone trees). Prof office hours could be a problem because they were usually quite limited. I can remember many times trying to see a prof, coming to his/her office, and there would already be a lineup of students waiting--frustrating. We did receive syllabi at the beginning of each term listing reading assignments, when papers were due, tests, etc. Somehow it all worked--we all managed to get through without email.

Oh man, this question makes me feel old. I was also an undergrad in the early '90s at a state school in California.

Honestly, there was just nothing that urgent. Our profs would publish the reading list at the beginning of the semester and you would know ahead of time what to read. If there were changes then those were announced in class or on a bulletin board. Same went for test scores which were typically posted up for everyone to see.

If class was canceled it would be posted on the door and you wouldn't know ahead of time. If you knew people had the same prof earlier then they would tell you that the class was canceled.