Once upon a time, a coworker angrily confided in me that no one from work was coming to her party. I stupidly replied, "Well, it's probably because none of us are REALLY friends. We're just coworkers. Do you really want people to come to your party that don't really want to be there?"
She quickly replied, "When you get invited to a party, you should go." Needless to say, I attended said party I had been planning on getting out of.
I have since learned that she's right. Go to parties when you're invited. It really means a lot to the people planning it. And it's good for you, too.