You have to make lesson plans for as many topics as your flight instructor requires? If you are asking about the checkride, you have to be able to teach any area within commercial and private PTS and the fundamentals (principles of flight, etc), all are fair game. There are certain areas that are required to be tested. You aren't required to teach all of them, but you may not know for sure what you are going to teach, depends on the examiner.

Some instructors teaching in a classroom setting may assign students with certain lessons to prepare, and then allow the students to "share" so everything is covered in the end. I've found it can be painfully obvious when someone is using a lesson plan they did not develop though.

Lesson plans should be just that, plans, not complete information on a subject, that should be in your head, in the books you are going to use, and so on. Try not to "tell" anything or use commercial sources that don't trace directly back to the PTS, look it all up in the appropriate reference as part of the lesson, airplane flying handbook, etc. I'm not saying to not use stuff outside of the FAA resources, but don't use a jeppeson book that simply restates what can be found in the appropriate reference, because that can leave the student clueless as to where the information really comes from. Make sure the student gets actively engaged. Handouts and aids can be good supplements. The more you teach and the more frequently you teach, the less you may need a lesson plan, but you are starting from the opposite situation usually.

Teaching takes practice, that's why it's a hard checkride, so prepare as much as possible and practice! A good idea during any of is to keep telling yourself: "Teaching isn't telling"