Scan textbook before you go to class. Read both for ideas and for details. Make sure you understand how the text is organized. READ your assignments. Look for main ideas.
Every lecture is important.
Think about the subject before you go to class so that you can anticipate what is going to be discussed in class. Pay attention the entire time you are in class. Concentrate on the lecturerer, not on how many holes are in the ceiling. Listen with your mind not your emotions. Take complete notes.