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.
If an online business, you need to go into detail how you will attract customers to your website. General statements like "I will use Face Book ads and email marketing" will contribute almost nothing to helping your cause unless you have detailed statistical analysis of tests you have conducted or of another similar business you have been associated with. If you do not have any data upon which you reference your estimates, it could show lack of proper thought to the remainder of your business plan.
This part of the plan details the features and benefits of your products and services, their seasonality and life cycle, as well as any future products and services you are planning. It also includes a thorough market analysis, in which you will study your customers, your competition and the market itself. Here you should include a PEST analysis, in which you will consider the impact of various factors upon your business. The factors include combinations of the following, depending upon your business: social, technological, economic, environmental, political, legal, ethical, and demographic.
Projected Financial Statements: These statements are usually helpful, but not necessary. You will develop and describe your strategies for the business throughout your Business Plan. In the financial section, you will need to estimate the financial impact of those strategies by developing projected Income Statements, Balance Sheets, and Cash Flow Statements.