There are a number of ways of going about the process of writing a good business plan. One of the most tried and time tested ways that works well is using a business plan template.
Maybe it's okay as an assignment for an MBA class, but it would be just too confining and irrelevant for today's fast-paced business environment. Anyway, you're ready! You've thought about this business venture for a long time and talked it over with friends and everybody agrees it's a great idea. Best to strike while the iron is hot!
Description - What product(s) or service(s) are you offering specifically? Are any patents, copyrights, or trademarks needed? Have they been acquired/filed? What is the size of your business? Where will it be located? Will this require purchasing or building a facility? Will this require leasing a facility? At what cost? Has a lease been negotiated? What personnel will you need? Where will you find suitable employees? What equipment do you need? Will it be purchased or leased? What are the qualifications of your principals? How do their backgrounds promote the success of this venture? Why do they think this will be a successful venture? Possible Data Sources: local Chamber of Commerce; community colleges & local universities; local employee leasing company; real estate agents; US Patent & Trademark Office; US Copyright Office.
While these are easily available online, some of them are way better than the others. A lot depends on the approach that goes into writing the business plan.