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".
The reality is no matter how much you work with things in your head, no matter how confident you may be and how much you think you already have a great vision for your business, there are so many great reasons why you should get it down on paper.
It seems to have been put there to fill the need to attribute a certain sum to marketing. Make sure you are researching each point of your budget, make sure that you are giving it context and it makes proper sense within your overall plan.
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.