When meeting strangers, it's best to find common conversational ground. What are people talking about? If you're not on Twitter (free), you better get with it. Conferences almost always use Twitter hashtags, so you can search what attendees are tweeting about. This will give you a sense of the conference's main themes, which make great conversation starters.
Some custom-conference apps also have a social stream for attendees only – another good place to get up to conversational speed.