Research Your Competitors (But Don't Copy!) Every business plan should focus a lot on the business's potential competitors, because research and analysis of the competition effectively gives you plenty of useful information. It may guide you as to where you should be advertising and marketing, or certain strategies to use or ones to avoid because you see they have been used unsuccessfully by others.
Contextualise Your Budget : Of course your budget will be extremely important. But sometimes people sort of pluck figures out of thin air, not giving it the context it needs in the business plan to make real concrete sense of how that budget is going to work.
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.
You can concentrate so much on essential financials and supply logistics, but overlook other issues like marketing or opening times. By showing the plan to someone you trust, they can have a look and see what might be missing or worth developing more. Getting that valuable second opinion on how robust your idea is will put you in a much better position to start and keep going successfully.