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.
If you need to get going quickly to ride the wave of a fad before it fizzles, then fast, bare_bones planning may be all you've got time to execute. This works best when you've already got the infrastructure in place, perhaps from previous projects or an established business, and you can simply shift energy and resources to the new idea.