I am, believe it or not, mostly an introvert. I think I went to my first ACS conference (2005, San Diego) and did not meet a single person that I did not know already (actually, that's not entirely true. I seem to recall meeting a senior grad student from Pitt. Nice guy. Can't remember his name.) I did a little (a lot?) better in 2008 in Philly, but not too much. Now, I think I could just spend time talking to people, the next time I go to a conference.
Introduce yourself. This is probably the hardest thing to do, some ways you can do this are:
a. (Hold out your hand.) [Say your name] from [Insert Name of Your Institution], and you are?Believe it or not, I actually will mentally practice what I'm about to say, when I talk to a new person. I'm glad that Kiyomi has informed me that I'm not the only one.
Follow up: And what do you do?
b. Hi, I’m [say your name] from [Insert Name of Your Institution], I really like your dress/purse/speech, etc. Make sure you really like what you are complementing people about, never be insincere.
c. Find a friend who is outgoing and get them to introduce you to everyone. (I once met 30 people in one afternoon this way.)