Start taking notes when the professor starts talking, even if you're only giving your notes a title. Circle unfamiliar words or words used in unfamiliar ways and make a note to find out what they mean. Learn to differentiate fact from opinion in lectures. Your ideas can raise important questions and make your notes more interesting to read. Develop your own set of symbols to identify or emphasize various items in your notes.
Every subject has a vocabulary that can be easily abbreviated.
Always take notes during discussions. Some professors lead discussions so that the students will make the important points. You are responsible for these ideas, too. The material that YOU get in class will make the difference, often between letter grades, and someone else's notes are no substitute. Always let your professors know when you will have to miss class, and they will often be able to help you catch up and study the missed material.