Cover all bases. Before embarking on your plan it is a good idea to undertake some research in to what a professional business plan should include. You can then use this as a check list to make sure you have covered all the relevant areas. Sections of the business plan should include information on the company, the product/service market, competition in the field, management team, marketing strategy, operations and financials.
Business plans may target changes in perception and branding by the customer, client, taxpayer, or larger community. When the existing business is to assume a major change or when planning a new venture, a 3 to 5 year business plan is required, since investors will look for their investment return in that timeframe.
Executive summary- The executive summary is the backbone of the business plan and it should include a brief background of the business concept, company's objective's or your plan, ownership structure, management team, service offering, target market(s), competitive advantages, marketing strategy and high-level financial details like expected profit, required funding etc. It helps the bank or finance executives to get an idea of your business.
Finally, a business plan should be error - free. This is important because your business plan defines who you are as a business person. If it turned out sloppy, then that does not speak too highly of you.