How are you doing? For an starter

Or just comment anything he or she is doing, examples I remember: To the girl with the coffee stall, in a very quiet corner of a bustling square: Whoa! How did you got this oasis of calm in between all this chaos?

To the same girl: I used to buy coffee in a stall like this when I was working in (other place) and it was beautiful, do you work for the same company maybe?

To the girls that were waiting for the bus late at night, while I was a bit drunk and eating chips and fried chicken: Hi there, do you know how to get back to (my neighbourhood), it's my first time around. Next: do you want a chip (they did)

To the group of girls sitting with one of my friends, first greet my friend, then ask: Can I sit here? (Yes, of course) How did you know (my friend)?

After starting with one of those, use questions that give you more information about the other person.

Where are you from? How do you know each other? What do you do for a living? (to be always followed by the interesting) What do you do when you are not (over-the-top-description of his/her job)?

If the situation that you are not comfortable with is starting a conversation with a random girl in a bar (which is very difficult), start with normal people you have short forced interactions with (shopkeepers are best). Always start with a greeting and be polite, try to notice which questions lead to boring conversations and which ones lead to fun ones.