While I still recommend the business planning process, I caution you to realize that a beautifully crafted document does not always equal business success. I've worked with many entrepreneurs who successfully launched without a plan, and some with beautifully written plans that never materialized. You and your business idea are unique. Your planning process will be unique as well. Be wary of one_size_fits_all advice or pronouncements from experts about how you should proceed.
Organization and content of the business plan will evolve as it is prepared. For example, if the driving force of the plan is marketing or sales then a preponderance of the analysis and plan_of_action section will be more up_front and sales oriented in tone. With business plan's the world is your oyster; think from the center out to the edges and think outside of the box.