How do I get talking to a girl?

Last night I was out in a bar in Shoreditch (Central London) with a few friends. There was a pretty girl working behind the bar and after ordering a drink I smiled at her, she smiled back at me in an interested kinda way but was then distracted because of taking an order from some customer.

I kinda realised that I had no idea how to deal with that type of situation. Like, the music was so loud in there that she wouldn't have really heard much of what I was saying, but even if it wasn't, I'd have had NO idea what to say. How do I start a conversation with a random girl (e.g. in this situation)?

If it changes anything at all, I have added a link of what I look like. I know I'm not the best looking chap but please tell me what I could do to make my appearance a bit better.

I don't have sufficient posts to make links but please copy this into your browser thing:
img62.imageshack.us/img62/5518/16860126075861204316220.jpg

Thank you :)

bump.. please? :/

Your picture link doesn't work.

Just walk up to her and start conversation.
It's not that hard.

I have updated the image link. Please have a look

In that situation, you probably aren't going to start a conversation; she's there to work and smile at people and probably gets hit on all night long.

Hit on women who aren't working at the club/bar, you'll be better rewarded.

If I were you I would go for some facial hair. Goatee maybe and change up the hair.
You have potential.