Just say hi, you have to have the confidence to start the conversation with a genuine expression or emotion, chat up lines just make an awkward situation. As to where, it depends very much on what kind of girl you want to meet. For example, in London 90% of the girls are chavs, but at the same time you can get into areas (e.g. high street ken) when all the girls are middle class, they won't be as "slutty" I guess, but I'm personally more likely to get on with someone when they can speak English properly.
Make sure you hear her talk before you start anything, don't follow her around if she's quiet, just do something that doesn't necessitate a long conversation that you won't be able to get out if she's an utter chav, e.g. brush past her and apologise.
