If the the tourists are interested in the city, then there's obviously something interesting about it. So you go to them and tell them about the city.
If there are some historical places or monuments, or some places to go out in the evening, good beaches (if it's on the seaside), good restaurants etc. From then, you direct the conversation the way you want it...
Edit:
You can "catch" them while they are looking at something, wondering what it is... You approach them and say like: "You know, that was made by... / that's a symbol of... / that's a good place for..."
You get the idea.
