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.
But do not be too paranoid, make sure you are showing it to people you trust, whose feedback you welcome and can be genuinely useful in guiding how the plan takes shape. Very often when working as individuals we get very close to certain details and miss out a big thing that has slipped your mind.
Have An Overall Vision : When writing your business plan it is really important to have an overriding vision of what your business is going to do, what it is going to be, and what you want to achieve. Very often it is tempting to get straight into the technical details, the monetary concerns, financial matters, where you will be sourcing supplies, etc. Now all these things will be vital in your business plan, but it has to be held together by a coherent, broader vision.
Don't Make Assumptions About Customers ; To be an entrepreneur does require plenty of self-confidence, sometimes almost a bloody-minded determination to make your business work. But this confidence spilling over into thinking that you know what 'the market' wants can be dangerous, without checking that it's true. You need to do your research that the market does ultimately want what you will be offering, whatever products or services you will be selling.