Hey there,
I definitely know how you feel. In fact, if you read my HSC journal, you could see me ranting about my math teacher and how she wasn't the best teacher. It depends on how you define as a 'bad' teacher. It's either you just don't get along with them or they don't teach anything. If it's the first situation, then the best way for you maybe ask for help from another teacher or even your friends. If it's the second situation. it's a bit more complicated.
Firstly, just ask around your class if anyone's actually absorbing content from the teacher. In my situation, I had a lot of people who had tutoring but our general consensus was that we didn't like her because she was always confused whenever she would teach us and then the lesson ends up being taken over my another student. And unfortunately, I had to find other ways to keep up because one thing you should keep in mind is that you shouldn't get carried away with the idea that you don't like the teacher. I had to be proactive and teach myself the content in advance because my teacher never explained things properly. I also asked friends from Year 12 (I was in Year 11 at the time) for help and even asked my classmates for help. I also talked to my dad about the issue and he called my school office, the Catholic Education Office, the junior school assistant principal (because she knew my family quite well) which led to her speaking to my school's assistant principal which ended back to my math co-ordinator. At some point, my math co-ordinator would sit at the back of the classroom and observe the class dynamic. I was actually lucky we had a different math teacher in Year 12 (who was better but hasn't taught 3U maths for four/five years) but even then, I went around and asked my physics teacher for help.
I guess my point is that when you don't like your teacher (regardless whether you just don't like their personality or they don't teach), the best way is to be proactive, whether it's just asking for help from friends or another teacher, or even teaching the content yourself. It was very stressful for me (it was actually so stressful where someone could literally come up to me and say "Hey, how are you" and I would just cry because I was so stressed) but the thing that I learned from the two years of dodgy math teachers is that I need to take initiative of my own learning because (unfortunately) at the end of the day, I'm the one sitting the exam, not the teachers.
Hope this helps!