Good misdirection:
"People always ask me how I'm good at magic, and let me tell you, the best magicians use misdirection. I supposed I'm only good at magic since as a kid I was always distracted easily, for example, this one time in school I was --Squirrel!"
"So you choose your card right? Completely free choice? No, don't tell me your card. There is no way I know your card, correct? For the first time ever, what was your card? etc."
Personally, I don't actually have set patter that I would use 100% of the time, try to just go with a conversation and try to:
use questions that make them think usually works best with "do you remember your card?"
take their mind off things "How's it going?"
crack a joke "So I'm now legal drinking age, I walked into a bar yesterday, and now I have a splitting headache, I tried a ice compress, but it still hurts. I don't know if you notice, but there should be a mark right about here."