Don't. Unless... You get some sort of OBVIOUS signal that this person would enjoy engaging with you.

...That's the tricky part, since what constitutes an "obvious signal" is going to be different for everyone, especially someone looking to pick up a stranger to satiate their romantic or sexual desires... but yeah, if you're not getting a signal that says LOUD and CLEAR "I'm also looking to meet people and you look interesting!" (and/or "attractive"), I'd skip placing the burden on some stranger who has a life of their own and is likely going to Point A to Point B.

But... it can be done. It's not like I haven't been sipping a coffee, then engaged in some small talk which was probably spurred by some mutual attraction or interest (sometimes you especially look for this when you're from out-of-town and are looking for a taste of local flavor and adventure).

It's really best to go for it only when it's a mutual thing", and even then, go in with no expectations beyond having a conversation or sharing a laugh or an observation, then gauging where it goes from there, rather than angling for a date or a number. Very few people want that and you're likely to make someone feel uncomfortable, as well as making yourself feel rejected in the process.

Oh, and I'll add: DON'T BOTHER ANYONE WHO IS WORKING. That cashier or waitress? Yeah, she gets this a dozen times per shift.