I often see people split into two camps. On one hand those who almost ignore competitors in their business plan, because they do not want to think about the issue yet and feel so confident they have a great idea for the market regardless. But I recommend not being overconfident when it comes to competitors. They are still there for a reason, they are still around and in business for a reason, so view them with that in mind.
However, business planning is an ongoing process and it should be updated regularly to assist in forward planning, the challenge for the entrepreneur while preparing a business plan is to communicate his ideas and identify gaps in management information about their business, competitors and the market.
When I have received business plans, the very best responses come from people who have looked at the risks and have an answer for every question. What you never want is to throw a scenario at your plan and have to answer "I don't know what I would do in that situation". You want to plan for every possible contingency, and certainly all the major risks to the ongoing success of your business.
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.