On average, a good business plan will be about 15 to 20 pages. Keep it concise but detailed. A good business plan will pay dividends both in the short and long terms. An investor and/or bank manager will see this and if the plan holds up well, then this will bring you the business that you seek. And from a personal point of view, a great business plan is something that you can return to time and again as a good reference point - something that you can draw upon in the future.
However, a good business plan defines one's target market, the class of people he intends to sell his products to, how to reach them, promote his products, in addition, defines one's market mix- people, place, product and price. People- this defines the people involved in the promotion one's goods and services. Product- this defines what one's goods and services are. Place- defines the location which also includes the means of delivering the goods and services. Price- defines how much one's products and services are worth in the market which will enable him analyze and evaluate his return on investment (ROI). A marketing and strategy tool defines one's business strength, his weakness, his opportunities and threats. It plots a graph that helps one reduce cost while maximizing profit.