The first was the word limit, though this was not, in a way, a new development.
Until this point, there was an effective word limit. Take a three-hour examination and divide by the number of questions you were required to answer. Three hours and five questions meant thirty-six minutes per question. How many words can you write in thirty-six minutes? There's your word limit.
Now, at University, you were asked for a specified length and were liable to be penalised if you ran over the limit.
Lesson Number One: Avoid padding.
The second new element was the bibliography. This may not have been entirely 'new'; students might have been asked for some indication of what they'd read on the way to the Senior History paper, but now it became a formal requirement, with some titles on a particular topic more or less obligatory.
Lesson Number Two: The size of your bibliography is an indication of the breadth of your reading on the topic. Therefore, bigger is better.
The third new element was the requirement to add references. It was no longer enough to indicate that you knew that this person or event played a role in that outcome. You now needed to show where that knowledge came from, acknowledge that mileage will vary, and indicate a familiarity with different interpretations.
In general, one did this through citations, which, in turn, came in two basic varieties. One was the Harvard-style reference, where you provided an author, title identifier and page number, within brackets, directly in the text.