I'm sure someone else somewhere probably has a similar technique to this, but I thought I'd share anyway.
This is a technique of my brother's. He's engaged now, but has always been a natural (douchebag lol). This was one of his main approaches.
The tricky part is, she has to take an interest in you first. Won't work for me as well as some because I'm not that great looking lol.
Basically, once you've established a couple of times that she's looking over at you and you've made eye contact a couple of times (the latch), find a reason to walk past her, to use the bathroom, go for a cigarette, go to the bar etc.
Do this around 3 times, each time she will hope you approach. A little addition I made is that, if you can, find a reason to stop right next to her the last time you walk past. Check you're phone or something.
By now she should have given up hope. Now make your approach.
Simple but apparently effective. I've not field tested this myself yet so if anyone wants to, I'd appreciate feedback.
£: GeMiNi :&