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!
Firms that are successful in marketing invariably start with a marketing plan. Large companies have plans with hundreds of pages; small companies can get by with a half-dozen sheets. Put your marketing plan in a three-ring binder. Refer to it at least quarterly, but better yet monthly. Leave a tab for putting in monthly reports on sales/manufacturing; this will allow you to track performance as you follow the plan.