Busy pubs and bars can be a great place to meet people; you can push forward to get a drink just to get closer to someone cute you've spotted at the bar, you can 'accidentally' bump into each other and you can get a conversation started on the flimsiest of excuses. Opening gambits such as "Excuse me, could I just squeeze past you to get to the bar?" or "Gosh, it's busy in here tonight isn't it?" are far better than the worn-out "Do you come here often?".
If all that sounds a little too proactive for you, you can simply people-watch. A friendly smile and a moment's eye contact will show anyone who takes your fancy that you're interested in getting to know them more.
