There are probably a gazillion things to say, but here are some general pointers.
1. Bathe. Seriously. I can't tell you how many times I've gone to a convention and had someone (usually male) go by and waft of eeeeeuuu-when-did-you-last-take-a-bath??
2. Dress appropriately. Sure, wear your favorite t-shirt with a silly saying, Dress up as your favorite character, but use common sense. If you're 300 pounds, don't wear spandex. Wear enough so that you don't get yanked aside and be told to cover up.In fact, please please please use a mirror, or ask a friend who can be honest, if your outfit looks okay. Unless you don't mind the comments, make sure you're not wearing clothing two sizes too small. And oh yes, you really shouldn't wear t-shirts with profanity on them. It doesn't impress the actors, and peeves adults who bring kids. If you do a LARGE con like Comic Con, wear comfortable walking shoes or else you might end up with plantar faciitis (I speak from experience!)
3. Children. The old adage of children shoudl be seen and not heard can apply to a degree at cons. If you go to a convention, remember that many actors like to tell stories that might not be appropriate for children. Babies should simply be left with a babysitter, because a) they can scream at the wrong time, and b) if that diaper suddenly needs changed, you'll miss out on the talks while you run off to fix the problem.
4. Bring enough money. Cons are not cheap. Not really. Most Creation cons are at airport hotels or sort of locked in, and the food prices can be high. if you can afford it, stay at the host hotel. This means you can stay up late and not risk getting flattened by an SUV while crossing the road. It's simply a matter of planning ahead. I have seen fans just literally flat broke at the end of a con and wondering how they'll get home. Scary.
5. Food. This depends on the con you attend. Some have food stations (can be pricey), others have restaurants, others you're on your own. It's always wise to bring along some snacks and bottled water. If you go to a Comic Con, yes, bring survival rations, cuz they are HUGE cons.
6. Sitting in the Audience. Sounds simple, doesn't it? But so much can go wrong. The people behind you who can't stop talking, the ones who insist on yelling out something to EVERY question. Believe me, the rest of us do NOT want to hear it.
7. Don't be a snob. That may sound weird, but it happens. You're a Stargate fan, but you ONLY like Daniel Jackson. Don't diss other fans if they like Jonas Quinn, etc. etc. While yuo can say you don't like something, don't put it down like "only idiots like that," etc.
8 Have fun, but remember that in this day and age, nothing you do or say in a public place could end up on YouTube. Yes, people take photos left and right, take videos, post this stuff on the net, so if you call in sick and your video shows up on YouTube and your boss finds it....
One of the best ways to have fun at a con is to go with a friend, or meet up with fans you've met on the net, etc. In other words, socialize! And oh yes, if you like to buy, bring a comfy backpack. Comes in handy for bringing back the loot :)
Okay, onward to the big stuff, the actors, producers, etc.
1. Actors are people. They are human beings. THey are not action figures to hug, grab their ass or other parts of the anatomy, etc. without their express permission. Many actors may shake hands, but try to feel them out (not literally!) if that's okay. The men usually don't mind, but women may be a little more less touchy. And for heaven's sake, if you run into any of the celebs in the bathroom, let them be!! The facilities is NOT the place to ask for photos or autographs or anything else!
2. The false sense of familiarity problem. As fans, we know a LOT about the actors. Iti's all over the web. Actor A has a chihuahua named Spike, he likes to run and eats Chinese on Sunday morning. If you run up to an actor and start blathering all this, it might unnerve them. They know zip about you, after all. So, show common sense. There are fans whom the actors do know (the fans do a lot of cons). However, do NOT abuse this informal relationship by taking up extra time in autograph lines, etc. .
3. Q&A sessions. They are for the benefit of ALL the people in the room, so please don't a) ask the actor to sing happy birthday to you or yours (especially if the actor doesn't want to sing or can't sing - yes, some cannot sing, believe me), b) tell them how much you adore them, etc. etc. (save that for a fan letter) or c) insist on giving them a present. Q&As are a finite time period. Those types of things eat up precious that a fan could have asked a question. When asking questions, don't ask boxers/briefs. Unless of course you want to tell them what YOU wear first *cough*. It is also NOT the place to sing a song to the guests (cringing at that fan at Comic Con last year or before- argh!) Ask a sensible question. Don't start your question with a lengthy preamble that goes on for two minutes. Don't ask "Why should I watch your show? I heard it sucks" (Yes I heard that question once!). Ask something you'd find interesting to hear the reply on, and something you think others might know. Stay away from personal questions of the actors. ALso, the actors can't recite an episode word for word, or remember what was on the table in episode #202, etc. .
4. Autograph lines. Don't ask the actor to sign your boobs or butt (it's just, well, tacky!). Don't ask an actor to sign fan fiction (particularly slash - just cuz you like it doesn't mean they like it even know what it is!). Many cons have rules on what can be signed, so check before you go to the con to make sure you don't drag along something that can't be signed, or to make sure you buy something that can. Even if you're shy, this is basically your one real chance for a brief one-on-one chat, so if you like their work, tell them that. They do appreciate knowing that fans like what they do.
5. Photo Ops. Well, it's up to you what you wear. Or don't wear, etc. Many actors are fine with just side by side posing, and others will ham it up immensely. Depends on the con, on the actor, on their frame of mind. As in rule #1, make sure you wear deoderant and spare the actor an unpleasant experience (not to mention the rest of us) and ladies, don't overdue the perfume ;)
6. Those pricey lunch/drink things. Many cons are now doing 'yes, you can have a one hour drink/lunch/brunch with so and so and 8 other fans.' These cost an and a leg (hundreds). Let's say you can afford it. Just don't monopolize the actor with questions (and this goes for the cheaper 'dessert parties' too).
That's about it. I did this quickly, so I'm sure I missed something and have no problem updatnig/correcting, etc. So much is just common sense. Remember that while the actors are there making an impression on you, you too are making an impression on the actors, producers, dealers, etc.
Oh, and if you take pictures, bring batteries. buying them at a hotel can be $$$$. Rechargeables are good.
I've done a lot of cons, both pro and fan, and have seen the best and worst in both. Some conventions are more like events (Creations - everything ala carte, expensive) while fan cons like Shore Leave etc. have more paneling, more stuff to do. And one huge huge reminder. NO actor/guest is guaranteed to be a convention, even if you shelled out $$$$ to see him/her. They all have it written in their contract that if they have conflict (i.e., a job) they can cancel, and frankly, wouldn't you rather see your favorite actor wokring than at a convention?
Anyway, that's it. Feel free to add comments below or tweet me at wraithfodder at twitter.
Ah, here's a good guide too! http://www.stevebacic.com/w_conguide.shtml.