There are multiple openers you could use. Approaching a group you could say "how is everyone doing tonight?" An individual, "how is your night going?" I used that one on a girl at a bar once and it sounded natural and got her talking. those are very basic but can be effective because it sounds like you aren't trying too hard.
You could try a harmless opinion opener which works almost every time such as, "do you know where a good bar is around here?" Or you could say some other place like coffee shop, dance hall, restaurant, whatever. Anyone who doesn't answer that in a somewhat respectful manner is just rude and you don't want to talk them anyway.
My advice if you are just starting to approach, go as basic as possible. Keep it simple. Too much clutter in the mind before approaching can clog your mind and make you overthink.
