At this point, you may be tempted to skip writing a business plan altogether, viewing it as an unnecessary exercise in jumping-through-the-hoops, suggested by some old business professor who probably never held down a "real" job anyway.
Executive Summary - One to three pages that summarize all the information to follow; come back and write this last.
Organization - How is the business structured? Who are the principals and the principal shareholders? What authority does each principal have in the venture? What are management's qualifications? What is the job description for each position? What does the organizational chart look like? Possible Data Sources: on-line templates for job descriptions & organizational chart.
If you know all of these except for Marketing, say, then this is where you will need to invest some time and effort. You can find a wealth of information by utilizing the traditional data sources such as chambers of commerce, major cities' websites, trade associations, the US Census Bureau, trade journals, magazine and online articles and advertising, etc. Performing keyword searches on Google, or Ask will bring up websites to check out. Following are some places to start: