I teach that you should seek to learn from competitors; obviously never copy another business's idea or what they are doing, but you can absolutely learn from their mistakes or see what they are doing and discover ways to improve it. All of that analysis belongs in your business plan: make sure you have your competitors under the microscope and make sure that is a solid chunk of your plan. That is some of the best research and information you will gather about what will make your business successful in future.
A business plan is simply a plan of what your goals are for the business, and how you plan to go about accomplishing them. Some people refer to it as a vision for your business. I like to refer to it as a blue print or a road map to accomplishing your goals. Your plan should be spelled out in clear and defining terms and be kept simple. It should be a written document and used as a tool in managing the business.