Several people have mentioned going to Worldcon and it being their first con, or first big con. Here on
Making Light is some excellent advice for the newbie.
To which I will only add, to the writers among us:
1. Don't take your 500 page ms to the con expecting to hand it to an editor unless that editor has already invited you to do so as a mutual convenience. You might get a chance to meet editors, you might get a chance to talk to editors, and they might invite you to describe your novel. Great! Usually what happens next is they say, "It sounds interesting--send it to me at work."
The chances are that you'll see and hear editors, but not get close, because several thousand other people are trying to get a portion of their time--including their pals from fifteen years ago, who've traveled all the way from another continent and here's their only chance to face-visit.
2. You can learn a whole lot by attending program items featuring editors. These panels can be the most useful career booster of the con, so take a notebook and pen. The editors on the panel will tell you what they're looking for, what they're not looking for, and all kinds of other nuggets of inside info. You cannot get more immediate data on buying trends than this!
3. If you find yourself at a party with Famous Editor from Big Publisher, you might get a whole lot more out of the experience by listening as they speak informally to a circle of people, than by trying to edge in and claim their time for your project.
4. If you do see one alone, look into their face. If their eyes are tired and their faces stressed, do them a favor, and yourself a favor: wave and pass on by, even if you've been introduced. It probably means they were up until three this morning, after three hundred conversations all day and night yesterday. You do not want to be talking to someone about your cherished project of years in the making to someone who is feeling like two week old kitty litter, and desperately needs caffeine.
In short, if you don't go with the expectation of making that fabulous connection at the bar that results in a six book offer on the spot (and such things were rare even back in the boom years) you'll have a great time just meeting interesting people and learning a whole lot about the SFF world. Cons are tons of fun--inspiring--tiring--nothing else like them. But you do need to go in sorta knowing what to expect and what not to expect.