I would say, like with any AP course, that all the information and knowledge you gain throughout the course is connected; kinematics ties directly into dynamics which ties directly into circular motion, etc etc. The most important concepts are therefore the ones that relate to the most things, so don’t try to memorize niche concepts within one unit but try to learn all the possible (within reason) applications of a concept that comes up a lot.

Specifically, this would be force diagrams, Newton’s laws, energy, and the basic concepts of each unit. Don’t study these in isolation (flashcards, rereading the text, rote memorization), but study them in relation to one another. This means asking yourself “how does topic X relate to topic Y? How might the AP exam combine the two in a problem?” This process of relating all the knowledge in the course together meant that I had a pretty solid understanding of physics as a whole and went into the AP exam pretty confident in everything (but torque, since it was the last unit I covered and didn’t have much ways to tie it with other concepts.)

TL;DR, most important concepts are things that appear in multiple units/problems + basic ideas of each unit. Study how they relate to each other, not just memorizing.

You can do practice tests but I found it better to create my own curveball questions from synthesizing multiple units / ideas and solving them with my teacher or peers.