Taking notes helps you concentrate on the lecture. Also, taking notes activates your tactile sense, so that you are more likely to retain the information, especially if you review your notes soon after the lecture. Take notes consistently when listening to lectures, and adopt or develop a note-taking system that works for you. Decide what is important. Listen for repeated terms or ideas.
Speakers use repetition to emphasize important points.
Watch for gestures and facial expressions that may also be used for emphasis. Listen for signal words or phrases. Listening for signal words will help you listen for ideas. Signal words can help you understand relationships among ideas. Watch for them as you read textbooks, and listen for them during lectures.