Someone sent me this question on Quora. Comic-con can scarcely be described, it must be experienced, but here's the crib notes.
It's a circus, really, where everyone who attends has the chance to participate. It fills the halls and the stairwells, spills out onto the sidewalks and streets, jams every corner with the bizarre and unexpected. It's a whirlwind of color and sound. It's massive and throbbing with life. It's the bar in Star Wars where people from many worlds and time periods collide. It's green hair and ray guns, steel claws and robots, Doctor Who and Game of Thrones, Goth and Middle-earth. It's every genre imaginable colliding and reforming into something completely new. It's manic. It's glorious. And I wish that everyday life embraced more of the freedom of imagination that's kindled there.
A few words of advice:
1. Wear comfortable shoes. Nuff said.
2. Plan ahead of time and be prepared to wait in line. Look at the schedule and figure out exactly what you MUST see. If it's a panel, get in line at least 2 hours before it starts. If it's in the 6,000 seat Hall H, get in line at least 6 hours ahead. People camp overnight for Hall H. I got in line at 5am for the Doctor Who panel that started at 12:30pm and was one of the last people they let in the door. If there's something on the floor you want to see, go there as early in the con as you can because you may never make it there later.
3. Be prepared for sensory overload.
4. A masquerade tip. If you want to see the masquerade but don't care if you sit up front, avoid waiting in line all day by showing up just before it starts. There are always seats left in the back and you can walk right in. And there are huge video screens throughout the hall.
5. Bring snacks and water. Sometimes it's impossible to get to food if you're waiting in line or running from one place to the other.
6. Bring a poster tube.
7. MAKE FRIENDS!! My experience at Comic-con over the years has gotten more fun because I now run into people I know. If there's something in particular you are a huge fan of, hang around the booth a while and talk to people. Get cards. Give cards. Talk to people while you're waiting in line. Comic-con is a huge gathering of geeks if nothing else, and you can always find someone who shares your interests.
7. Don't expect to see everything. Don't even try.