Before you leave:
  Right, time to sound like your mother. Have you got everything you need? Ticket/confirmation of booking for convention and accommodation as required? Suitable ID/proof of age as listed by the convention organisers? All the other things that get left behind (wallet/phone/phone charger/favourite stuffed toy etc)?
  Yes, I know it's obvious, but check this stuff anyway. How obvious it is that you need something is directly proportional to how much of an idiot you'll look if you forget it.

Getting There:
  If you're going by car, do you know where you're going, and have you checked about parking facilities - the venue the convention's being held at may only have limited parking. If you're using public transport, do you know how to get from the bus/train station to the venue? Do you know where to tell a taxi to take you?
  On public transport, buy a return ticket. If you're coming by car, when you get near the venue, fill up with petrol before parking. This way, even if you spend all your money at the convention, you still have a fighting chance of getting back home afterwards.

Registering:
  Make sure you've got whatever is required for registration easily available. Registration is one of the most hectic times of the convention, so you may have to queue up for a while.

At the Convention, DO:
*Have Fun! You're there to enjoy yourself, so make the most of it!

*Find out where alterations to the timetable for events and video showings will be posted - there's bound to be some, and you don't want to miss something important because you didn't know it had been moved forward an hour.

*Check out the dealer's room reasonably early on - some of the stock will be limited, and when there's several hundred people with money burning a hole in their pocket, it can't last.

*Remember to actually eat and drink. I mean normally. Living on nothing but Pocky and Smirnoff Ice for three days is not A Good Thing. Ditto for remembering to sleep and wash.

*Mingle. Circulate. Meet chicks. Talk to "some guy". You never get this many anime/manga fans in one place normally, so make some new friends!

*Get stuff signed by Special Guests. In necessary, buy a relevant DVD in the dealer's room. Autographed stuff's cool.

*Balance your time between video showings and events well. Remember, you can watch anime anytime - don't stay cooped up in one video room for the whole event.

DON'T:
*Bitch at people if things aren't going absolutely perfectly. Conventions are run by volunteers, and they don't like people shouting and screaming at them. Especially as they're probably working 18-hour days.

*Leave your gear lying around. There's always someone who'll pinch stuff.

*Letch at cosplayers. Yes, she's gorgeous. No, that Cutey Honey outfit doesn't cover her up so well. Grow up. Cosplayers like showing off their outfits, so if you want a picture of someone, just ask, and they'll probably be quite happy to pose for you. And don't even think about touching anyone who isn't your girlfriend/boyfriend. The security guys will stand there grinning while they beat the shit out of you.

*Abuse people on stage, especially in the cosplay masquerade. It takes some serious balls to get up in front of that many people, so even if you think they suck, applaude and cheer with everyone else.

*Take drugs (Or drink, if you're underage). You'll get kicked out.

*Swap badges, abuse staff, trash your room, break con rules or generally be a prick. See above.

Gophers (Volunteer Staff):
  If this is your first con, I'd advise against volunteering to help out. Bluntly, it's bloody hard work, and you could well find yourself a little lost.
  Always remember that the Gophers and convention committee have given up a lot of their time to organise the con, so bear with them if they seem a little stressed ;-). If you had a good time, let a committee member know if you spot one. They'll appreciate it.

After the Con:
  If you have any feedback or complaints about the convention, email the committee or post on the convention's forum. Going on random forums saying "This con suxxor" will not win you any friends with the organisers if you couldn't be bothered to talk about it with them.
  Childish bitching on the internet in general should be avoided - any anonymity you think you have is an illusion, and convention committees have long memories. If you've got an issue, talk to them about it before running your mouth off.