Keep It Simple
Every company should have a mission statement. A brief, anyone-can-understand explanation of why the company exists and what it aims to accomplish. It's setting vision for everyone working there, but also serves as the continual goal to achieve.
While "mission statement" may sound corporate-y, it helps to have one for yourself. It may be less vision and more goal-oriented, but it's important to lay out what you hope to accomplish both in your daily life and long term.
That being said, it should be no longer than one or two sentences. If it takes a company 30 minutes to adequately describe its vision, there could be a lack of focus. "To make the very best, most natural blueberries," would be a great mission statement for a farmer. It doesn't encompass every minute detail of the work, and doesn't have to. Keep it simple. The clearer the goal, the easier it is to achieve.