A quick note on being social.

Do not, I repeat, DO NOT be that girl.

In the grand scheme of things, it really is important to maintain an image of a sociable person. If you are invited to a gathering, the worst thing you could possibly do is sit in a corner and not say a word.
It doesn't matter what people are doing at the event, you should do it too. If it is something that you simply cannot take part in (hard drugs or orgies, for example), either relax and open your mind to it, or simply excuse yourself and leave. If it is something like playing a card game or having a conversation, take part in it.
By not taking part in the activity, not only are you making it obvious to everyone present that you are not comfortable, but you are making them uncomfortable too.

In case you are particularly socially awkward, here are a few tips that will ensure you never to become "that girl."

1. Read the newspaper everyday. Even if you only read the front page, you can bring up a topic that others will likely know about, which will lead to a decent conversation. News conversations are generally not ideal, but it could lead to other, better conversations.
2. Know the group dynamic. If you know that the people you are hanging out with hate your other friends, do not mention them. Try to find out who is dating whom, who hates whom, and who has fucked whom. It not only keeps you from saying things that will piss people off, it helps you know whats going on when people start gossiping. When they do, you must offer an opinion. Do not say, "Well I don't really know her." Nothing bonds people better than agreeing on something evil, like how fat someone got.
3. If people are drinking, drink. If you are not a drinker, you have no business being at that particular gathering. If people are not drinking, you should leave because that party sounds lame.
4. Do not criticize someone who is at the party. For example, do not say, "Maybe you should slow down, you've had 13 beers." The only time it is OK to do that is if you are joking with someone. Never tell someone to stop drinking if you are not really, really good friends with them. Also don't say anything negative about the gathering. Don't criticize the music, the food, or the crowd.

I found it necessary to vent on this particular subject. It's crazy to me that some people just don't know how to be fun. If you stick to these tips, people will not likely talk shit about you when you leave, and you will probably be invited to another party of theirs.

Heed my advice: Do not suck at parties.