Do you have a solution or any best practices to make ads work for clients in small cities with small audiences?

I do marketing services. I run ads for people. I have copy I know works, I used it on several clients. What happens is when I get a client from a small city, it has a very small audience. So the lead ad usually doesn't work. I tried a bunch of stuff and I never actually could get it to work, so I'm wondering if you have any solution for that...