I did basically what the directions say- PoochieBells® Official training Method | Poochie-Pets
Except that I don't use any words for going out like those directions say. When the dogs went to the door to go at first I just let them out, and because the bells are on the door they rang. After a little bit of this the dogs were already associating the bells with going outside so we moved on to step two. Then when the dogs signaled to go out I encouraged them to put their nose near the bells, when they did that I let them out. Eventually I only let them out if they rang the bells, and that's what they do today.
At the time I had a foster dog that caught on the day I hung the bells, maybe he had seen them before, or maybe he was just into bells, but it literally took him going out twice to ring them. Copley took about 36 hours and Kerri took about 3 days to consistently ring them. She didn't like the bells on her nose so she bats at them with her foot, I think that's what took a little longer.