Before starting, you should gather as much information as possible. The first place to start is by visiting with other CSA farms in your area to learn from their experiences. You can visit Local Harvest to find a farm near you. It also helps to start small and gradually build your customer base. You may want to start by pulling together a group of community members who are interested in community supported agriculture. This core committee can help you decide what items to offer, how many different types of share memberships to offer, whether you should offer (or require) a work component for members, and how many weeks your membership should cover. Your core committee can also help you get the word out about your new CSA.
Here are some additional links on community supported agriculture that might be of assistance: