Run a classified ad in your local newspaper and post fliers around town to let people know you're looking to form a group of singers. Specify the number of people you'd like in the group and which style of music members will sing. If you have a gender or age group in mind, mention that, too.
Schedule auditions with the people who respond to the ad. Ask people to sing a song of their choosing. If your group will sing a particular style of music, such as pop, require that the people auditioning sing that style so you can hear how well they do.
Select finalists from the people who auditioned. Welcome the finalists back for a second audition if you still need to eliminate candidates.
Schedule a group audition so the finalists can sing together. It's important to make sure the group members' voices complement one another during harmonies.
Notify the people you selected that they made the cut for your singing group.