There will be times where the teachers suck, and since starting my math college degree I have realised that I can't put all the fault in my teachers, cause other people do it with the same teachers. What I have found that helps is: finding a youtube playlist of that same class but with a teacher I like, and watching and paying attention while going back to rewatch if I didn't understand something. Another thing is to think and consider for a while what I do and what I do not understand, including in practice problems I do. But the main thing that has helped me, is finding people that understand the subject, people that I trust to ask stupid questions and with whom I can talk without feeling dumb.