1). Start going in on a regular basis to the point that she at least recognizes your face.
2). Once you are fairly confident she recognizes you, start making friendly small talk.
3). During one of these friendly exchanges, when the time feels right, go for it. Ask her out. JUST DO IT.
Just make sure you don't wait too long to carry out the above steps. This shouldn't be drawn out for months. Women like confidence, so don't dilly dally. At the same time though, it would probably be best to wait it out for a few visits so you aren't some completely random dude. Your chances of success probably increase with time, but at some point you'll surpass that time limit, if that makes sense. Either way, you need to do this man. She might shoot you down, but that's fine. You have to take risks dude. Otherwise you'll have to live with the regret that you never even tried.