Approach with a reason that has nothing to do with her beauty or you finding her attractive. Complementing her beauty gives all your power away. Approach with a comment on her fashion choice if she's wearing something unique. Other approaches could be commenting on her mood, or what she might be up to - always preface it with something like "I saw you walking here just now and I noticed..(launch into your comment)". First step is how she respond to your opener, and proceed from there if she's receptive. You keep making comments and observations until she hooks on something or starts giving you information about herself - this is a buying signal. Your comments can be anything from her accent, her mood, or what she looks like i.e. "You look like you know how to dance, you've got a dancer's physique". Dancing is subconsciously sexual so it's good area to lead her mind to.
Once she hooks and gives you information e.g. "Actually, I love dancing. But I'm not a professional. Tehehe" then that's your greenlight to proceed to building some rapport, giving her a bit of information about yourself and then flirting with her. Flirting can be done through push/pull statements (but this has to be very calibrated), body language and light kino like touching the back of her elbow when you're emphasizing something you're saying. The power of touch is very lethal if you do it the right way.
You only proceed through these stages if she's attracted, and a girl makes it pretty obvious when she's attracted.
Once you've done these things then you could either try for an insta date by suggesting she accompany you to coffee (you were already getting a coffee and she can come along - never ask her "Would you like to get a coffee with me?"). If you don't want to insta-date her then you can either leave her with your card James Bond style, or take her number.