Always start with "Hey"
Then, if she was looking at a certain article of clothing, comment on it.
Example:
Me: Heyyy (smile)
Her: Hi
Me: Checkin out some skirts huh?
Her: Yeah, gotta get some cute ones for summer
Me: You know, every man loves a girl in a skirt, but you know what I think is even better?
Her: haha Whats that?
Me: A girl in a classy skirt. You kinda strike me as a classy lady
Her: Oh really now?
Me: Yes, as a matter of fact, you do. I happen to be working on being a classy kind of guy, so I've got an invitation for ya...
Her: What kind of invitation?
Me: Well, obviously I'm here doing a little shopping, and I need a female opinion on a few things, so I figured you could help me out a bit. (wink)
Her: ha I suppose I could do that
Me: I knew you'd be down for that, who knows, maybe I could help you pick out some classy clothes, that way you could toss together an outfit the next time we get together
Her: Hmm. Sounds like a good idea, and when exactly are we getting together?
Me: Oh thats a suprise.
Her: Mmm. I like suprises.
Me: Haha I bet you do. (check watch or cell phone or osmething with the time on it)Oooh. Bummer.
Her: Ooh bummer what?
Me: I told a friend I'd meet him 15 minutes ago, I hate bein late. Hey, you should write your # down, and I'll give you a call about this whole, shopping thing (wink again)
Her: Awww, well thats not a bad idea
BAM. Number.
Keep it going from there