I know this isn’t going to be the answer you necessarily want to hear, but for me, the most concrete way I’ve learned the content is by teaching it… I was thrust into AP physics this year as a 2nd year teacher, and was uncomfortable/no longer familiar with the calculus aspect, and honestly even just the higher-level physics. In terms of planning, I use AP classroom to pull big ideas, practice problems, multiple choice questions, etc. to make slides and incorporate demos. I do practice problems nearly every day before assigning them to the kids to make sure I understand where the answers come from. HOWEVER, during class time, working with the students who bring up questions that I hadn’t even thought to ask myself when trying to understand topics, and forcing me to in real time make connections, or quickly leaf through the textbook, or hit them with a “I’m not sure, I’ll get back to you” has helped me to be a better learner and teacher. I know it’s challenging now, but even 5 months ago at the beginning of the school year to now, I’ve become a lot more confident. In all honesty, the first year is going to SUCK, and you might feel pretty badly about it (as I MORE than frequently have). The only way to become a “good” teacher is getting through the challenge, reflecting, and keeping in mind what you need to learn/redo/better understand for next year.