Like anything else in business, a business plan should be judged good or bad not in a vacuum but in its business context with its specific business objective. Most of the online discussion about business plans is focused on business plans related to seeking investment, and I`m going to make the assumption in this answer that you are asking about those.
By having a written business plan that you`re regularly reviewing, you can make confident decisions. You`ll have all the information necessary to know when you can hire new employees, launch a new product line or make a major purchase. At the same time, you can also plan ahead in case a decision doesn`t work out as expected, minimizing your potential risk.
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.
Why? Because once you know the details of your business inside and out, you will be better prepared to write your executive summary. After all, this section is a summary of everything else you`re going to write about.
Write your plan using language that your audience will understand. Accommodate your investors, and keep explanations of your product simple and direct, using terms that everyone can understand. You can always use the appendix of your plan to provide the full specs if needed.
People who read your business plan will already know a little bit about your business because they read your executive summary. But this chapter is still hugely important because it`s where you expand on your initial overview, providing more details and answering additional questions that you won`t cover in the executive summary.