Well as 20yr old guy I have learnt your first impressions make the whole conversation.

So saying “Hey” isn’t really the best.

But banter and slight teasing can work better. Let me make an example.

Let’s say I see a beautiful girl by the bar with beautiful longhair that is clearly her own hair.
I walk up and say I love her wig and from there it’s humour as long as she can laugh then I know the guard is dropped. If she’s with her friend I involve the friend and say your friends wig really looks good.

You can do this approach in different ways it can be a comment on the drinks , dress, shoes etc anything as long as you can find a way to tease a reaction out of them

But again delivery and confidence matters but as long as you having fun with it then it all comes naturally.

(EXCUSE ANY GRAMMATICAL ERRORS. English isn’t my primary language)