I play the piano for this choir and I know a lot about music. I even sing myself. But I've never studied how to teach a group of people to sing before. I'm at a loss because these people don't sound very good. Any suggestions?
If you're willing to take on the task (and it won't be easy!), you have to start with the basics. If they won't learn to read music, you'll have to teach them their parts by rote, playing each individual part over and over until they learn their part.
Once they've learned their parts individually, you need to get them to put it all together. Some of the best ways I know of to do this are
1. count singing — everybody sings the rhythm of the song by counting out "one two ti four / one-and two-and ti-and four-and", etc. "Ti" is used in place of "three" becaue it flows out more quickly in rhythm without that tripthong in the beginning. At the beginning, count-singing should be done without pitches so that the singers are concentrating on RHYTHM only.
2. Once the rhythm is properly set in their head, add count-singing with pitch (but still no lyrics). This will help set the melodies and harmonies in their heads.
3. Chanting — again, this is a rhythmic exercise, but helps set the lyrics straight with the rhythm. During this phase, work on setting and correcting diction, making sure consonants (especially final consonants of words and phrases) all fall together. Proper diction during singing is one of the most important aspects, and is almost universally ignored by church choir directors.
4. Put it all together.
One of the most useful things I have found for my own practice is the creation of rehearsal tapes. This is a tedious process, but is becoming more practical with the advent of sheet music scanning software. I can scan a song, convert it to midi, massage the midi file somewhat with a music notation program, and create usable rehearsal tapes reasonably quickly (about 15 – 20 minutes per page of music these days). The trick with such a process is to create a separate rehearsal tape for each voice part, isolating that voice part on one channel (let's say the left channel for convenience) while mixing all of the rest of the voices to the right channel, and mixing the accompaniment equally. This way, each singer can hear their own part clearly without confusion from the other voices, but while still hearing the accompaniment.