Learn to be funny!
Me and a girl in the back of a car, my friend is driving, his girl is in the passenger seat. We started naming favorites.
Girl: Hey, what's your favorite color?
Me: Clear
Girl: Clear isn't a color you goof
Me: If you don't stop making fun of me, I'll turn this car around right now young lady.
Girl: *shocked expression* You aren't driving so I can say whatever I want. *sticks her tongue out*
Me: Oh no? Haven't you ever heard of a back seat driver *smerk on my face*
Girl: *Laughing* - gives me a kiss on the cheek "That's for being cute, AND making me laugh."
Theres more to that story, but thats an example.
If you're meeting a girl for the first time, she doesn't want to have a stupid conversation like she's in a classroom, or like shes talking to her older brother. She wants to laugh and have a good time. Show her one.
Avoid negative statments (self bashing included), religion, politics, and ANY relationships.
NEVER EVER ask if she's single or has a BF, EVER.
You aren't supposed to care about that. What you care about is making the sale, rather than the lame sales pitch. If she's seeing someone, she will let you know. Play it off for as long as you can! Girls lie you know. Show her that you wanted to talk to her because YOU wanted to, not because you think she's single.