The book How to Write a Local Church History by Dr. Frederick E. Maser gives a good overview and can be borrowed for free through the Internet Archive's Open Library (sign up for a free account to borrow it!), or physical copies are available for purchase from the General Commission on Archives and History.
The most critical part at the start of this project is to determine the goals and scope of the history, and determining who will do the work.
1. Create a working group of individuals interested in the project who will provide the guidelines and support for the various pieces of the history, and define the goal and scope of the project. Ensure that this group is representative of your church and that people with a variety of skills are included. Carefully decide on a projected budget, as there will be costs associated with the research, writing, and publication, even if much of the work is by volunteers.
Goals: What do you wish to accomplish with this project? Who is the intended audience? How will it be distributed: print or online; and available for free or for purchase?
Scope: What is the time period to be covered? Which elements of the church history will be explored? Will this be a textual history or do you want to create multimedia in conjunction with any written content?
2. Decide who will have the major responsibility for the research and writing, and who will oversee the budget. This may be a single individual or a group of people. If your budget allows, you may consider the possibility of hiring someone to research and write the history, rather than using volunteers. If you decide to hire someone, and your working group does not have a particular person in mind:
3. Develop a plan for executing the project to ensure that the work is done. Create a project timeline and assign tasks.
Congratulations, you are on your way!