I currently have a small private voice studio but I would like to see it grow in numbers. Has anyone found a method or methods that have worked? Even ideas from instrumental teachers would help a great deal!
My mom teaches voice and piano as a side gig at a performing arts school. Since you have your own studio, you don't need the space in a school, but you could hook up with whoever the biggest dance studio is in town, unless they already do voice lessons too. See if they will let you put flyers and business cards in their studio, and offer to let them do the same at yours.
Also, check places that people have to frequent – like grocery stores and laundromats – to see if they have bulletin boards. I've seen a lot of them that do, and people just stick their business cards and flyers on the boards.
Where I live, most casual, small, locally-owned restaurants these days also seem to have a place for business cards near their registers. Try that too.
And of course, if you have any music stores in town – the kind that just sell goods and don't offer lessons – they will probably let you put your cards there.