Attention to detail. A plan that is concise and clear reads professionally so don't make yours too wordy. The reader needs enough detail and information to be able to make an informed decision. As with all professional documents, care must be taken to avoid spelling mistakes and use correct grammar and punctuation. A plan that makes absurd or unrealistic assumptions is of no use so stick to the facts and make sure you are making credible projections and accurate content at all times.
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.
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.
It needs to have a list of everything you need. Note that the word everything here comprises of the equipment, technology, raw materials, financial and other resources that you may need when starting and running your business venture. Having all these listed will give you an idea on how much capital you need before you start and how much money should you make in a day to make your business survive.