If you ask, you shall recieve.
If you haven't talked to her:
Go up to her, say hi, ask her if she's new.
She'll either say yes or no or whatever, investigate more about her answer, then proceed to tell about how much you've been there.
3 minutes TOPS of conversation, not more, if the conversation is still one, try to cut the conversation short even before the 3 minutes, signal to her to follow you to your excercise or whatever and keep talking.
The point is, after brief intro and all. Rinse, then repeat. Rinse again. And then, tell her you're out, give her your cell and tell her to write down her cellphone for you two to go out again:
"Hey CuteHB, write down your number, so we go out sometime".
Don't make a big deal out of this, you're just asking her for her number.