This video out of the United Kingdom does a great job in just a little over 3-minutes in describing the basics of what you need in the business plan. I have previously shown videos about developing a business plan but this video shows how a business plan should be laid out and the importance of each section.
Again, a business plan is just not a document you use when first starting up, but it is a living document that you will need to update on a regular basis.
Your competition will change and so will the marketplace. Your business plan should reflect the changes in the marketplace and your competitors and how you will deal with those changes.