Marketing Plan is a planned implementation of marketing resources to achieve marketing objectives. This means, Marketing Plan is a systematic process in designing and marketing of marketing decisions. The marketing plan will focus on information gathering, information dissemination formats and the structure of development and coordinating the company's strategic and tactical responses.
You can't do a marketing plan without getting many people involved. No matter what your size, get feedback from all parts of your company: finance, manufacturing, personnel, supply and so on--in addition to marketing itself. This is especially important because it will take all aspects of your company to make your marketing plan work. Your key people can provide realistic input on what's achievable and how your goals can be reached, and they can share any insights they have on any potential, as-yet-unrealized marketing opportunities, adding another dimension to your plan. If you're essentially a one-person management operation, you'll have to wear all your hats at one time--but at least the meetings will be short!