The best openers are made up on the spot and range from relating to the situation at hand or are totally random off the wall quips.
1) Hitting on a new Cashier where you frequently shop.
You: Hi, haven't seen you here before.
Her: I'm new.
You: Reach your hand out and introduce yourself.
Her: She will automatically respond with same.
You: That's why your apron (or whatever uniform) looks so good
You: You make that apron look good.
You: I bet you'd look good even if you had nothing on.
Her: She will blush or tell you to shut the front door.
You: If she blushes, ask for her number. If she tells you to shut the front door say, "What? You're not used to compliments?"
Her: You're rude!
You: No, just honest. You're beautiful and need to be complimented often!
2) You: Hey! Wow! Never thought I'd see you again!
Her: Do I know you?
You: You forgot. We went to different schools together!