Talking about how to touch a tit properly.

I assume that "of course anybody knows how to touch a tit". The point here is How to do it in a way it's sexually enticing for her? I have not been with lots of girls but with the previous one this haven't been a problem. Nowadays, when it comes to caressing my partner boobs, sometimes feels like, for her, is more a relaxing massage than a sexual thing. And I know how to do it as a relax massage when I want. But I must've been doing something wrong when looking for excitation I'm getting relaxation. So, here I am, looking for a good piece of advice or any useful tricks.

Edit: I'm reading lots of post with the message "Ask her" "Talk with her " etc.

Just to avoid anymore of those answers:

We've been together more than 15 years.

Of course I have talked with her about this, and not just one occasion but plenty of times.

I am asking here because I am looking for some kind of tricks. Maybe someone with a similar situation could help.