I was just discussing this with my assistant instructors the other day.
They usually come in with a good idea what they are going to teach, or look at my classes and expand upon what i am doing.
I myself, it depends. Sometimes, I come in with a clear idea of what I am going to do...only to have it change drastically by questions or the levels of students present.
I teach such a wide range of ranks that most of the time my plans go down the tubes, and I wind up going with the flow.
So I guess my answer is....