A smart man once said it - If you are failing to plan, you are planning to fail.
I do believe a good business plan is the foundation to any successful venture. Without a plan how would you know if you achieve your goals? And how will you set your goals in the first place?
Not only that but while compiling such a plan, one will face questions they haven`t even thought of, questions that will
affect the future of the given project. Answering those questions beforehand will give you a good preparation of what lies ahead...
suggested, a SWOT analysis is something quite simple but very effective. I can also recommend trying some of the numerous online softwares for help on this subject. For example I`ve used BusinessInABox and it does give you a good outline of the topics you need to cover in a good marketing/business plan