Lecture notes are most important to me the second and third time I teach a particular class. The first time is exciting, the text might be new to me, and the butterflies surrounding that always makes the class exciting and terrifying at the same time. The important thing for me, if it's going to be a class I teach multiples times, is that I take my lecture notes from the first class and build from them. Simplify, add things, try new angles. The class should get better every time you teach it.