Read up first about starting a museum. This is not a simple venture. Get a copy of "Starting Right: A Basic Guide to Museum Planning" published by the American Association for State and Local History.
Consider joining the American Assocation for Museums to help you during your start-up phase. Through this association, you can eventually receive accreditation for your museum.
Research museums in your state and area and visit as many as you can. At last count, there were 17,500 known museums in the United States. Take note of what you like and don't like, and ask as many questions as possible of the curator and staff.
Determine how you will secure your collection. Are you using your own private collection to start the museum, or will you rely on donors?
Write a mission statement that explains what purpose your museum will serve. This will serve as a blueprint to help you plan a museum and decide what will be in the collection.
Decide what kinds of items the museum will display. Will the museum be a repository of local artifacts for your area, or do you plan to open a museum on a specific topic, such as a toy museum or farming museum?
Run the numbers. Determine costs, including location rent or purchase, utilities, personnel, insurance, as well as costs for setting up display cases and exhibits, advertising, licenses and memberships. Then you will have a good idea of the money the museum will need to bring in, considering government funding, private donations and possible ticket income.