Well, first we start with understanding the mission, goals, and objectives of the Mission Statement desired, Goals, and Objectives desired: the intended demographic, the desired message to convey, the emotion you want to elicit from readers, etc. Of course, that's based on the foundation of the non-profit itself and will be done through discussions with those providing input.
Having worked in Strategic Planning as well as owning two businesses, I'm very familiar with the importance of Mission Statements and the communication thereof to those carrying out the organization's mission.
Let's get started.