So this is probably a dangerous thread to begin my posting career at Obsidian, but I'm a gal who loves danger, so what the hell. Plus, having been the girl being chatted up at the bar, I might have some helpful insight.
First off, there are going to be women who are down or even looking for a "quick run through the sack" as taks put it, and those who won't be. With the former, you just need to worry about beating out that night's competition, which depending on the bar and the night might be more or less difficult.
If you either aren't sure whether a woman is of the above type or are willing to invest a little time in someone who might not end up sleeping with you until the third date...then my primary advice is listen! Walsingham is right about it being a good idea to sit next to her and her friends...but try to figure out what they're talking about first! This will give you much needed info on the best conversation piece to get into her pants.
Which brings me to the belief that "The Greatest Conversation in the World, Ever" is going to have to read a lot like a video game dialogue, with lots of conditionals. Which is good because we're all video game nerds in one form or another here, right?