The business plan is a necessary but not sufficient condition for finding outside investors. The plan describes the business and what it might become, and that`s all. A beautifully written, edited, and formatted business plan will not make a less investible business more investible.
The best use of business plans starts with founders using plans to establish strategy, tactics, milestones, and (especially important) essential projections of sales, spending, headcount, startup costs, capital needs; it`s for the founders to know, first, what they plan to do.
To understand your competitors and the industry, you`ll need to do market research. Invest time and effort and do market research correctly. A business can`t succeed if the owners don`t understand their industry, target customers, or the competition.
Projections are important not for their actual numbers as much as for their presentation of drivers, relationships between growth and spending, key spending priorities, sales aspirations, and assumptions related to cash flow. They have to be solid and integrated, but accuracy is much more a matter of transparent assumptions than accurately predicting the future.
All business plans should be reviewed and revised at least monthly. The review should include looking for changed assumptions and analyzing plan vs actual results with management of the difference.
There are tons of good outlines available, plus books, blogs. Down below I have some specific resources related to my work; but not now. There is no single best outline to use, but investors will want to know about the market, potential growth, competition, differentiation (or secret sauce) strategy, tactics, key milestones, important assumptions, the management team, and financial projections including use of funds, projected sales, income, balance, and cash flow. Use your common sense to put first things first and organize it all well.