A brief account of how the company began- You should mention in your business plan the history behind the formation of you company and the background of the founders and directors.
Operations plan- This section will include details of execution of the day to day operations of your business, location of your business and how it will benefit your business, HR policies of the company and the production plan if you are offering products.
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.
It also needs to be written in formal format and style. You have to remember that a business plan is something that you may have to present to your business partners, financial firms and banks. So if you can, refrain from using slang in any part of your plan.