1. Prepare music that suits the group and makes them sound better than they are. Too often the choir director will choose music that will require skill far beyond the talents of the group to pull off. This may discourage the singers and possibly offend the ears of the listeners. The opposite may be true, too. The music chosen may be far too simple and insult the intelligence of the singers. This is a delicate balance, but can be fined tuned and adjusted until the optimum balance is achieved. An occasional "challenge" piece can certainly be put into the rotation, as long as it is balanced with enough pieces that can be successfully learned in the little available time. The choir should provide musical numbers regularly, so a mix of easy to learn, moderately difficult, and advanced pieces need to be carefully planned. CAUTION: Hymns written for 4-part Mixed chorus and 4 verses long are probably the hardest to keep interesting and to sing well. Hymn arrangements usually have a variety of treatments of the hymn tune, including unison, 2-part, SAB (soprano, alto and men as long as their part is not too high), as well as 4-Parts, that might be more accessible for your group.
2. Divide the year into "seasons" - months that will have the hope of the best attendance. I have found that the "Christmas Season" is the most successful time of year to get support for a choir. Everybody seems to love singing Christmas music. The problem seems to be calendaring the actual performance dates before your group flies the coup. Try to get the those dates set well in advance of choosing the music. Then, be sure to get the performance commitment from your singers so you know which songs to choose aligned with voice part balance issues. Other times during the year, you can plan to sing once or twice a month and perhaps go on hiatus for a couple of months in the summer. You may call September through December the "Christmas Choir Season" and take a couple of weeks off around New Year. Then have mid-January through April the "Easter Season." Mid-April through June can be a "Patriotic Season" or "Family Choir" season, and so forth.
3. Form different types of choirs from time to time depending on the needs of your people. Each ward has its own peculiar mix of people. Some wards have a good mix of young, middle-age, and older people. Other wards heavily lean to the older set or sometimes are overrun with children. Some have no youth at all. But within each ward, there should be enough willing singers to sustain a choir of some sort. Some wards divide out the "seasons" of the year to give different groups the opportunity of providing music for Sacrament Meetings. Sometimes they have a full Mixed (S.A.T.B.) Choir, sometimes a Family Choir with voices of all types, sometimes a Relief Society (S.A.) chorus, or a Youth Chorus (S.A.B.) or even a Men's Chorus (T.B. or T.T.B.B.) or Children's (Unison or 2-Part) Chorus. They can prepare and perform for an entire season or just once, it doesn't really matter.
What really counts though, is having well-prepared, suitable, and beautiful music for the listening enjoyment and spiritual fulfillment of the listeners. When the effort is made, the group can feel successful and
that is how you sustain a choir year-round!