Teach the choir to read rhythms before doing anything else. Even if they can't read music, if they know how to read rhythms, the job of teaching them melodies by rote will be simpler. Teach them basic note values and have them clap rhythms while reading music. The whole note is worth four beats, the half note is worth two beats and the quarter note is worth one beat. Teach them what each note value looks like, and provide them with sheet music filled with simple rhythms. Start each session by clapping basic rhythms as a group.
Help choir singers learn the note names by providing them with a worksheet and some basic information about bass and treble clef notes. Teach them that the first line of the treble clef is an E and the notes that follow are alphabetical. Inform them that the first line of the bass clef is a G. Pass out a sheet of major scales, and have people sing the major scales as part of the daily warm-up. This will help them begin to associate notes with pitches.
In the beginning, while singers are still learn to read notes and rhythms, teach each individual part by rote. Sing each musical line to the choir, and have people sing it back. If certain members of a section learn the melody first, you can break up into smaller groups and have those members teach their section their individual parts in sectional rehearsals. This will take more time at first, but it is the best way to get a new choir singing quickly. When the choir is learning a new piece, create a schedule to meet with performers in each section as individual groups.
The pianist would normally play the accompaniment to the choir; however, in a choir just starting out, it is best to ask the pianist to play the individual parts. This will give the choir much-needed reinforcement and allow them to quickly learn their parts. The piano helps to keep everyone on track and in teaching individual melodic lines. This is especially useful since it is unlikely that the conductor will be able to sing each part in the correct range. The piano is able to play in any range, making it easier for the vocalists to learn their music.