A lot of the assumptions would be driven by by your background, study habits, and concern (for lack of a better word) over admissions.
APs - if you’ve taken an AP class, the classes are pretty much taught to the test, and teachers use old exams to prep the kids. You could use tutors during the course, but not for the test typically.
Subject tests - Again, if you took the subject tests (or Achievements in my day), you knew that you took it at end of your subject, typically jr year-end, and maybe looked at the old test for the format.
The studying for the next class is more on how concerned you are about admissions. Most kids that get an A or a B do not prep for the next course but I could understand prepping if you struggled in the previous class.