Thank you for requesting me to answer the question
I wont offer any general advice like check your syllabus, pay attention in class or get good coaching but I will try to teach you actually how to study so that you never forget
First Thing First, you can’t learn more than 10% in a lecture, it scientifically proved, active attention in class won’t help you
Second, there are a lot of books, have to choose them wisely, you have to make sure that you have your future goals ready, buy books on the entrance exam you are going to give, make sure that you to study entrance exam during 11 & 12 (you don’t want to stay at home while others are going to college right?), You are in medical so make sure you study NCERT book, this should be a main book and all others should be your reference book