From my single days....
The trick is to reinvent yourself from "stranger" to "non-stranger" in as few moves as possible.
I would come up with a nickname for a girl I'd like to talk to and then if a "chance encounter" came up (at the jukebox, at the bar) I'd tell them my new nickname for them. Then later (much later) I'd have another chance encounter and call her by her nickname from earlier. Like old friends having a reunion. It's golden.
Like if her shirt had glitter or something:
"Wow, you're all sparkly! That's my new nickname for you. Sparkles!"
Then just walk away. Next time you run into that girl, you call her Sparkles. Minimum incubation time: 45 minutes. The longer the better.
It works even better if you are good at remembering faces and you bump into her at the grocery store a few days later and you say "Hey! Sparkels! How did the rest of your night go last Saturday!"
Always use fun, flattering, cutsie names, not names like "big mama". If you aren't very quick-witted, you can just use something obvious like "pink shoes". "Hey Pink Shoes!" or if the pink shoes have exposed toes, "Wow those are some pink shoes! And I can see your toes! That's my new nickname for you, Pinky Toes!".
Speaking of shoes, a strange girl will always "model" her shoes for you if you comment on them. It's wierd how comfortable a girl gets when she thinks you are looking at her shoes with her. And it kinda gives her a little taste of harmlessly accepting physical flattery from you. It's pretty powerful. I think it is because most every woman has attractive calves and feet. There isn't too much variation from woman to woman, so it works equally well on all body types. A woman 150 lbs with nice calves and feet would LOVE a man to focus on her calves and feet. It takes away her self-consciousness over her waist.
There's my PUA lesson.
Those were the days!