Easiest way to pick up girls alone is at a place with a dance floor. Show up late, and if you're going to drink, do the majority of it before you go. When you get there, grab a beer and go right to the dance floor. Don't wanna look like the creepy guy just standing there by himself.
what he said.
Dont drink if you can avoid it. You want to be situationaly aware. there will be girls who are alone too. talk to them. more than 50% chance they are there to hook up as well. If they ask you why you are there alone, I always said,"to find a sex partner for the evening". It works.