With about a decade of experience in business advisory roles, and having reviewed tons of business plans, I have come to the conclusion that most of them are worthless exercises. Most people approach this task like homework in high school, emphasizing form over function, in this case with the obligatory pie-in-the-sky market assessments and hockey stick revenue projections.
I am actually not a big fan of the written business plan, especially for small businesses, because misexecution often betrays the benefit. The important thing is to be continually thinking strategically about the market you are competing in and your place in it. Are you competing in a market (whether goods or services) that people are willing to pay for? What is your unique niche? How are you adding value over what already exists in this market? This is a dynamic process (because the market is constantly adapting) so the worst thing you can do is "finish your homework" and forget about it.
My "business plan" as a lawyer basically consists of three principles. First, focus on a narrow niche (that I enjoy) and get really good at it. Second, continually assess the shortcomings in the market for my particular brand of services (for instance...what people hate about lawyers, which I learn by discussing the myriad horrible experiences people have had with them) and avoid falling into those traps. With those two under control, I now know that I have a business...I can add more value than most or all of my competition, so the next step is figuring out who I want to grant the "pleasure" of benefitting from this value. I don't want to be all things to all people. I don't want to work with just anyone who walks in the door. I identify my profitable and pleasurable clients and try to get more work from them; I also actively pursue similar businesses to these existing successful relationships, with the emphasis always overtly on "relationship building".
So my advice is...don't feel the need to complete some sort of lengthy exercise. What's important is the "process", which should be continual. There are only a few truly important factors that will determine whether you succeed or fail and you should always be reassessing them.
-- Danny Bronski