I used this along with LivePlan to write up a business plan for a competition. Made it to the semi-finals so it must have helped *shrugs* LivePlan costs money though; I was luckily able to use it as part of the competition. But I suggest you find someone in accounting/finances so they can look over that part of your business plan if you've never had experience with that before.
I am going to assume this business plan is for a bank or other some other financial backer. For this type of plan it is really important to demonstrate the viability and short term profitability of your business. It's good to start with a well executive summary, then move into details of the business market research, your development plan (short- and long-term goals and steps to reach them), and financials.
The executive summary should be short (a page or so) but informative and interesting enough to get the investor excited about your product. It's the written version of your elevator pitch. Make sure to include who you are, the name of your business, what you are selling, and how you will make the investor money.
The next section needs to describe your business in more detail. Talk about the product you are selling in depth, and discuss your business model and strategy. Include details about the structure of the company, ownership, and legal issues (like licensing and franchises). After reading this section, the investor should understand the ins and outs of how your business works.
The market research section is crucial. It shows that you understand your market. Include information about your target market (size of market, physical location, demographics, etc), the market you are working in (economic, political), your competition (How saturated is this market? Who are you competing against and how are they doing business? What are their strengths and weaknesses?) and your competitive advantage (is your product better than the competitions, or less expensive, etc).
Your development plan should cover at minimum an outline of how you plan to grow your company over the next two to three years. This should include all of your important goals (opening day, x number of customers by this date, second location by this date, etc). Goals should be measurable and realistic.
Financials are where most people are going to flip to, and they'll be the area of expertise for most investors. You want to make sure that you include projected cash flow and balance statements going about as far into the future as your development plan. You may want to get professional assistance preparing this section, because this is how investors will decide whether you are going to be profitable. You will want to include a current net worth statment for your business (all assets and liabilities) and, if you are applying for a loan, personal assets that can be used as collateral.
That's all I can think of offhand. Hope this helps.