That forces you to stay actively engaged in the lecture. Take detailed notes on your reading , leaving plenty of room to add lecture notes to them. Ask the instructor if he or she is giving the same lecture at another time. Hearing it again will help solidify your understanding of the material and help you fill in gaps in your notes. Ask questions in class.
Many instructors allow time for questions.
Use this time to ask for clarification of difficult points or simply to fill in information you missed the first time. Most instructors will discuss the material in different words, perhaps adding illustrations, that will simplify the material. Adapted from Ellis, Becoming a Master Student . Houghton Mifflin Company, 1994.