hey mate. One of the most helpful websites I've seen is
http://www.wayoftheplayer.com there's a good article on there "the players guide to picking up women at the gym" I think you'll find that helpful.
I also was in the same situation as you it worked out for me I went out with the girl for about 2 months. The best advice I can give you is don't try to impress her don't be a gym creeper just be your regular self. At the end of one of the classes strike up a convo about something yoga related then as the convo progeesses ask her if she wants to get a coffee. That's what I did worked for me.
Good luck!