It is known to be the most crucial step in the successful running of the business because a well planned business venture carefully scans all the possible opportunities and threats, understand the demands of the market and arranges for the best possible resources which finally lead to the success of the business.
The first point to keep in mind about business plans is... have a business plan! This may seem obvious but is overlooked. Many people start businesses without a plan; sometimes it can come from sheer bravado, thinking "I don't need a plan", or alternatively you might hear "It's all inside my head, that's my business plan".
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.
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.