How do you set premise later if you couldn't set it early on in the conversation?

I have often been in situations where it is a group setting when traveling or I have been friends with somebody who was dating earlier but recently became available.

I am not looking for a cookie cutter answer. I have an idea of how to set premise or flirt otherwise, but setting premise later on in a conversation seems a bit difficult to me.

Probably because the way I naturally flirt would seem like it came out of nowhere if the premise hasn't been set earlier.