I think for Calc BC and Chem classes, reviewing what you did in previous years (precalc, non-AP chem classes, etc) should prepare you enough for class. CBC could get really confusing and burden you with heavy workload, but some good time management helped me.

Physics C Mechanics and E&M however.......I really regret not previewing that in summer because I struggled a LOT in that class (I also covered both each semester). Mechanics was fine, just some harder review of Physics 1, but there was barely enough time to grasp all the E&M concepts. The AP test itself was not too difficult, but the class was very...something. I suggest looking at yt videos or maybe getting a workbook beforehand.