Start by writing a description of your business, including what stage of development it is currently in (conception, start_up, first year, mature, exit) and your plans for growth. Discuss the nature of your business, the main products and services you offer, the market for your products and services, and how and by whom the business is operated.
Right now, growth may sound like an unattainable goal as businesses are grappling just to survive, but hey, "flat is the new up." If a business can keep its doors open and lights on, then it's doing better than many others. But lights and open doors don't make sales, so making changes that attract business is in a sense, striving for growth. It won't be this tough forever, but for now, putting some growth strategies into action may be what keeps your business alive, if not thriving.
Do not try to write your business plan in one sitting. As I mentioned in the beginning, for a traditional brick and mortar business, it could take in excess of 100 hours to compile all of the information needed into a comprehensive but yet understandable document. For online businesses, probably not that long. But your final product should be well thought out, well documented and easily understandable.
It may not be pleasant to imagine all the "what ifs," but doing it now and planning for those unexpected events will improve your company's chances of surviving a storm. For an excellent step_by_step guide on the details of developing a risk management plan, see the article "How to Develop a Risk Management Plan," by Charles Tremper at wikiHow.com.