Lesson Prep is time consuming and not the most enjoyable part of teaching. In my experience lessons work far better if you have constructed your own powerpoint, visual aids, handouts and questions,with reference to the the notes and lesson plans of the school you work for.
No two instructors would teach the same lesson the same way. When I teach I like to bring in pictures, video clips and anecdotes outside of the schools notes and lesson plans. This is what makes the difference between good instruction and students sat doing CBT.
There are moves afoot in the industry to replace Ground Instructors with CBT and we must strive to keep that extra quality of having a live human being in the classroom.
To do that Instructors must be continuously reviewing their material, replacing bits that didn"t work last time and trying new things.
JAR FCL1 reflects this need by limitimg you teaching to 23 hours per week, they appreciate the extra time needed for you to lesson prep.