Answer:
Most important thing to remember is to not procrastinate and never begin studying the day before the test. It will often be too much content to learn in just one day. You should always stay on task and complete all your class assignments and homework on time. To study, although it is time consuming, I would recommend reading the textbook thoroughly and either taking detailed notes or answering the questions clearly on a reading guide (if you're given those). Then I would recommend watching some videos on it to improve your understanding on the topic. Often take practice tests on the section you learned (you can find those online or possibly at the end of a chapter in your textbook) will help. If you have AP classroom you should try taking the progress checks as well.
If you already have a good grasp of the material you are being tested on, I would recommend buying the AP review books (Baron's and Princeton review are both good companies). Those books will hit all the key concepts that you must know and is an effective way to review for a test. Hope this helps!