The most important thing to consider when writing a plan is to take your time, be thorough, be accurate, and above all, believe in yourself and your product. Don't just rely on a sample plan, create a proposal that you're proud of, and that you are convinced will compel others to help you realize your dream.
In many cases business plans are very important but so much of the time it is a plan to try to convince someone else that you know what you are doing with your business like banks, investors, partners, etc. Now it is true that a well written business plan can also be a major benefit to your success as well if done right. It can guide you and keep you on track and can be the vehicle to get you were you want to be especially with so many outside forces now days that bombard you. A plan can be extremely important to your success especially when you look at the statistics that says 51% of small businesses fail sometime during their first 5 years.