Once you have a broad outline of the skills and sub-skills that you are going to teach, you can then move to thematic units. If you are aiming for a cross-curricular approach in your home classroom then a summary of themes should be added to your annual and quarterly planner. These themes will obviously cross over all of your subject year plans. If you are beginning with a broad theme such as the environment, then your resources for all subjects would be based on environment issues. Quite simply then, your English comprehensions and written work would be related to an aspect or aspects of the environment. In the mathematics class, your examples would be based on the environment, and so on.
Lesson plans are an effective tool in the hands of a teacher. If for some reason, a day is disrupted, you can simply refine or combine two lesson plans to cover the following day. A lesson plan must not restrict the flow of learning and teaching. If you have planned to cover a certain amount of work and fail to do so, there will always be an opportunity to move onto the concept in a follow-up lesson. Home school teachers who have difficulty being flexible, would be well advised to plan their work in lesson units and not individual lesson units.
Obviously, an effective teacher will plan for a whole phase or at least year to begin with. The best way to start the four step process to drawing up a lesson plan; would be to begin with a broad overview of the skills, knowledge and desired outcomes for each quarter of the academic year. One can simply plan to make a one page annual summary per subject to be taught. If you are planning for the years work in Language arts classes, for example, you could in your annual draft, plan to start the year with poetry, move onto the novel genre in the second semester, the drama genre in the third semester, and so on.