My number one tip is to STUDY! I know it sucks, but once you're in high school, it's going to become a part of your routine every single day. Even if you study right now, keep on doing it over and over and over. Trust me! It'll help. Also, get a tutor! Maybe someone you know is doing well and you could ask them to help, or you could ask a student who was in your class and passed. My number one advice is to just keep working hard. I get it; chemistry is HARD. You'll get there!
