It takes a while to make your own perfect note-taking system. The key is to identify the important and the less important information. First, be present in class. Second, there is no point in surfing the web or chatting with the peer next to you. A face-to-face session between instructors and students is far better and a more dynamic way to learn, than memorizing facts and dates in a book.
All lecturers provide clues to the most important topics. When you become aware of these clues, they can be helpful in order to take effective notes.