Practice fielding difficult questions and as a group brainstorm up clever answers to such questions. The new members will not know all the history and may want to bring up old decisions and will need to have considerable briefing on the status and processes of the group. New members may also have different ideas which can be a great resource to tap, especially as the longer term members begin to burn out. Many groups have created an associate member category, where new people can get in the queue for the project but are not full members. Usually this involves coming to meetings and making a payment.
Some groups have associate members get pre-approved for a mortgage of their target unit.
Most new members will need a fair amount of energy invested in them as they learn the community ropes. Assign a committee to do information sharing, or create a written account of the decisions and processes of the group. New members can be a large energy drain so be prepared to deal with their questions and lack of knowledge. The later in the development new people come in, the less they will feel part of the group because they will have less chance to impact the community development. It is easy to be impatient with new people, especially if they ask questions about established procedures and community norms.