Use an Anchor.
Look her over, and spot something about her appearance that you can comment on.
Start with her shoes, and work your way up.
Do not choose a physical body trait (like big earlobes, bubble-butt, or her giant breasts) to comment on. Especially not her overall attractiveness.
You find one thing that you can key off of and say something about that will give you an inroad. This is your ANCHOR.
Once you've found it, you comment on it to her and smile at her, making strong eye contact.
Example: She's got bright red shoes on. "Wow, those are... interesting shoes. My sister might like a pair liek that. Where'd you get them...?"
Example: She's got a black denim dress on. "My sister likes dresses like that. Where'd you get it...?"
(If you don't have a sister, use 'Aunt' or 'Cousin.' You don't have to lie.)
The typical question I get is "What if there's nothing out of the ordinary about her?"
Simple: You make something up. There is always something you can find when you look, and if it's not readily apparent, you make it up.
If she's got clothes on (and even here on in California, they still wear clothes) you can find something to pick out. I recommend looking for jewelry, because every woman takes a lot of thought in selecting her jewelry.