I tried most of these, but my grades are really low. What should I do? I'm really stressed about my grades and I need to get into a good university.

Before you take your exams, make sure you really know the material. Paying attention in class will not be enough. As soon as you know you have an upcoming exam, start studying an hour per night so you will be better prepared. Also, if you don't know something, ask! Even if you are embarrassed asking a question in front of your classmates, still ask your question, or if your teacher allows you to, stay after class and ask your questions. if you know you're really struggling with something, ask the teacher for extra help or hire a tutor.