Remember the proverbial expression 'not seeing the wood for the trees'? You need to see the 'wood' first, then delve in and start examining the individual 'trees', meaning the individual items which you will be breaking down later. So a great point is to make sure that you have that overarching vision - and if you cannot find one, then maybe it is an indication that you are obsessing on a few technical aspects that do not necessarily make up a whole business as you had imagined it.
If you are someone who shies away from planning, or you don't like writing or preparing documents, nevertheless you are going to have to force yourself on this occasion. I say that because it is such a key document for the future success of your business, such a tool throughout its development to return and refer to.
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.
So it is crucial that every time you mention financials in your business plan, to really give them the correct context. When I have worked with clients in developing business plans, there has been a budget or amount set aside for example to be spent on marketing, which has been decided a bit arbitrarily. I mean with no real research, no understanding of what that amount needs to be spent on, and what that budget will truly achieve.