Where do you start?

I think the starting point for a lesson plan shoudl be your classroom itself. Sure, you've got to start each year with a basic idea of what needs to be taught, but the driving force of the classroom should be the students themselves.

You cannot simply assume taht the same cookie cutter lessons you walked into your first day of tecahing with will last you until the day you retire. If you did you would not grow as an educator. 

You must first take into account how each of your students learn. Are there any students in your class who speak another language or have a learning disorder? What kind of learners are your students? Visual, Vocal, everyone learns differently and this will change how your lesson is taught.

After this take into account what your students enjoy. Are they on sports teams? What are their hobbies? What do they like to do for fun? 

Take all of this into account and you will have your basis for a fun and exciting lesson and an enjoyable classroom environment!