A business plan in 3 easy steps.....sounds like a challenge :)
1. Do a self-inventory of yourself and your business idea. What are your strengths and weaknesses?
2. Do some research into your competitors and the market you are entering. What sorts of opportunities exist? What threats are there to your business idea.
3. Ask yourself why your customers will choose to come to you over your competitors.
Once you have given these some thought, you will have prepared some essential information to the planning process. Your strengths and weaknesses, combined with the opportunites and threats in the business environment form what is called a SWOT analysis. Your plan should work around capitalizing on the opportunites by utilizing your strengths. Your plan should also address how will deal with your weaknesses and any threats that may arise.
Lastly, when you consider why a customer will choose you, this is part of your competitive advantage. It's the uniqueness of your business. Don't just say "because we cost less than our competitors". Basing your business advantage around cost competittion may work in the short term but, if the competition is agressive, it is usually the new guy that loses everything when sales are based upon price. In this day, although price is important, there are people who are willing to pay a bit extra for exceptional service and product quality.
Hope that helps you get started.