Via all around cool guy, Dave Kletcha, comes Diana Rowland's How to Network at Conventions. This has been a topic of conversation the past year among several people I know. Diana (whom I don't know, yet) does an excellent job of summing up the major points. It's also been on my mind as I gear up for World Fantasy.
The most important point, IMHO, is her second bullet, "Have Fun and Make Friends." Yeah, howdy, hallelujah, sell it sister! I was a complete idiot at my first con (World Fantasy in Madison, 2005, I hereby appologize to everyone I was a dick to). Now that I've gotten over myself, and embraced this concept, I enjoy cons a whole lot more.
Cons are really fun places, even bad ones. If you write or enjoy any genre that holds cons (SF/F/H, Romance, Chick Lit, etc) you owe it to yourself to try one out. One good place to start looking for SF/F/H cons is the Locus Magazine Convention Lists. Not all cons are listed every year, but most cons have websites and you can check previous year lists and click on the websites to see if they're continuing.