It does not have to be long or overly complicated. It simply has to have the elements required to put your goals into action. Developing a SWOT analysis (strengths, weaknesses, opportunities, threats) will help you to identify problems before they start. Craft your own or hire a business writer to create a dynamic plan that will guide your operations. An effective plan is one of the most important elements over overall business forecasting.
There are many reasons for utilizing such a document. Is the final document going to be about implementing a decision already having been reached or is it about analysis and recommendations for a newly proposed activity. As noted above, a finished document may be for internal or external purposes. Externally they are often used to solicit funding for a start_up or joint venture. Whatever the purpose, do not confuse effort with say, a marketing or a production plan.