I wouldn't sweat it too much. It's the sort of thing everyone needs to learn by practicing, that's how everybody who is any good at it got there.
If it worries you, maybe start with innocuous compliments, things like that whatever looks cute, you have a pretty voice, stuff like that. Don't have to press, you're not trying to get anywhere or anything, just build up some starter confidence in expressing yourself. Like the other guys said, if someone doesn't seem receptive, don't sweat it, just back off. Nothing wrong with a compliment.
It's a trial and error thing, though, and you'll develop your own style over time.
Then I'd just go with the examples the other guys gave, it's good stuff, and they're probably more current than I am. Banter is fun, you're doing really well if you're both laughing. I liked that shoulder squeeze litmus test thing one guy mentioned, that's a good move. Anything you can back off from pretty easily like that without feeling like a dick is fine.
We're all being vague intentionally, though, nobody can give a script for it. Any script is a bad script, it all just varies too much. Back to what I originally said, this isn't really answerable in a forum discussion, not well anyway. Everything has to be either really vague, or risk being wrong for you. And I'm not some self help guru willing to take that risk of giving advice that very well might not work, just so I can sell a book or get youtube views or something.