Do your research. In order to be able to write a strong, comprehensive business plan you need to possess a sound knowledge of the market you are involved in. You need to actively conduct market research and ensure that your plan makes reference to your findings. It should include factors such as market size, the predicted growth path of said market and how you propose to gain access to it. For example, if you are planning on opening a bar then your business plan should include figures based on the local population, cost of suppliers, predictions about whether the bar industry is likely to grow or decline in the area and a review of the competitive environment.
Business Overview- This section will cover the objectives, mission and vision of the business. The goals of the business should be properly outlined in this section.
This situation is complicated by the fact that many venture capitalists will refuse to sign an NDA before looking at a business plan, lest it put them in the untenable position of looking at two independently developed look-alike business plans, both claiming originality. In such situations one may need to develop two versions of the business plan: a stripped down plan that can be used to develop a relationship and a detail plan that is only shown when investors have sufficient interest and trust to sign an NDA.
Once you have done all this you should have a complete and detailed professional business plan. The most important thing to remember when developing the plan is to see it as a living document and include specifics regarding dates and specific responsibilities. Your plan will need constant reviews and updates and things change so expect it to be a work in process for a good stretch of time. It will all be worth it in the end, a well-written plan will help ensure that the business is fully focused on what is required to achieve the company's goal.