After doing it myself, and seeing several go through it.. I would suggest the following. Everyone has a different approach, and something else may work better for you.
Don't sit down and try to write them all at once, you will and up revising them and spending lot of time redoing stuff.
Create a Private and commercial syllabus, outlining the lesson plans in an order that you believe makes sense, make sure it allows for pre-solo and pre checkride required tasks.
Create a lesson template that you like and make sure it includes everything from the instructors handbook. Elements, equipment required, etc..
Create 2-3 of the first lessons you expect to teach for the private syllabus, take just those 2-3 and teach them to your cfi, go over the format with him. Go over your Syllabus' with him as well. Do not just show up and expect to teach something, you should be studying the material very well before attempting to teach him, otherwise you will just waste time and money.
Finalize the template and moving forward study and create 2-4 lessons, and teach them to your instructor on the ground. Bunch the flying ones together and do some flight lesson's on maneuvers that make sense together.
Before you know it, you will have a LOT of experience teaching the ground portion, the lesson plans will be completed by the time you are ready, and you will likely be in decent enough shape on the flying as well. You will have taught each and every private and commercial lesson plan, mainly on the ground but in the air as well.
Helpful hint, most of the commercial lesson's are similar to the private one's only the tolerances are different. (Landings, etc)