Suppose that instead of saying every word and writing every statement and drawing every diagram and deriving every equation in class, you were to put a lot of the material in class handouts that include gaps skipped steps in derivations, axes with no curves showing and exercises with spaces left for responses. Further suppose you announce that you will not go over most of the details in the handouts in class but any of it especially the gaps and questions could show up on the test. Most of the students will then actually read the handouts at least after the first test, when they discover that you meant it. This strategy accomplishes several things. By eliminating the need to say and write and draw everything in class, you buy yourself many classroom hours that can be devoted to the things that make learning happen spending more time on conceptually difficult material, giving more examples, asking and answering questions, and implementing active learning.
Several references present ideas for making such classes effective.
The larger the class, the more essential it is to use active learning. In a traditional lecture class with 15 students, it is not too difficult to get almost everyone actively involved in asking and answering questions and participating in discussions of course material. In a class with 40 students it is extremely difficult to do so, and in a class of 75 or more it is virtually impossible. Few students have the self-confidence to risk looking foolish by asking or answering questions in front of a large number of classmates, and the traditional pep talks proclaiming that there are no dumb questions and that wrong answers are also valuable generally have little effect. On the other hand, when a class is periodically given something to do in groups of two or three, the risk of embarrassment is minimal the only real difference between a class of 20 and a class of 200 is that the latter class is noisier during activities.