That way they'll feel ownership in the choir, and you can count on them to attend rehearsals. Know where each part will sit, where you will stand, and where the piano will be. Decide when your first performance will be, and how often you intend to sing. Have at least some plans for the next big holiday. Know what you're rehearsing, and have more than enough parts for the number of people you expect.
Hymnbooks are convenient for first rehearsals.
Sing through all parts until you know them. Know how fast you want to go, where you want to change dynamics and tempo. Finally, prepare yourself spiritually. This relaxes the singer, increases blood flow, and encourages healthy singing. Rather than bang out one part at a time, try playing two parts at a time.