Try this one bro, very simple and effective:

"Hi, how are you doing"-- with a smile, girls love it when a guy smiles, shows he's confident and fun.

She'll probly say "fine" or something like that, then just say:

"I come to the gym a lot and i've never been lucky enough to see you, is this your first year?"-- say this smiling as well, looking at her eyes, this is a good time to remember what color they are.

She'll answer and then you can ask questions about her from there. Then end the conversation by asking for her number.

Just be confident about it, and remember to listen to what she says and just focus on her face.

Good luck bro, i hope that helps!!!