I take notes in an outline format while the teacher is lecturing, then when I get home I try to fill in the details after reading the chapter in the book the professor went over that day. While doing this, if I don't understand something ask the professor the next day during her office hours or before/after class. Also, READ YOUR TEXTBOOK. I know it's boring and tedious but reinforcing your notes by reading your text will really help you understand difficult concepts. And of course doing your assigned homework also helps a lot.