So, here's a quick guide, purely from my own perspective, of how you can be the kind of convention guest who doesn't annoy people. This isn't the final word, just one opinion. And while I usually will say this isn't directed at anyone who might be reading this because I don't want to hurt anyone's feelings, I suspect that the people who most need to hear it don't think it applies to them, so let's just say that if you're absolutely sure this doesn't apply to you, that probably means it does (the ones it doesn't apply to are probably stressing over whether they might have ever done one of these things, even if they haven't -- and it's that kind of thinking that makes them good guests).
1) Don't be a panel hog.
I think this is rule number one and needs to be embroidered on throw pillows. Panels are like show business -- leave 'em wanting more. If the audience is intrigued by the things you said in a panel but wish you had said more, they will find you later in the lobby, bar, con suite or at a party to talk to you some more about the topic. If you hog the panel and go on and on and on, particularly if you keep the person the audience most wanted to hear from getting a word in edgewise, they'll be sick of you. Yeah, you'll have made them remember who you are, but probably not in a good way that will result in book sales. In general, each panelist should get approximately the same amount of time, but not all panelists are created equal. The more prominent panelists who are the ones the audience most likely is there to hear (bestsellers, award winners, the guest of honor, etc.) should probably get more of a chance to talk (that doesn't mean that if they're not chatty they should be forced to speak, but it does mean that the other panelists should allow them to get a word in edgewise and shouldn't butt in when audience members ask that person a direct question).
Corollary One to this rule: It's always safest to assume that you are the least prominent/important person on the panel (unless maybe you're a multiple Hugo winner, national bestseller, a Grand Master or the convention's guest of honor). Just because you haven't heard of the person, it doesn't mean that he/she doesn't have a room full of fans ready to hang on his/her every word. Even if you are more prominent, it's far better to have the audience directing questions to you because they want to hear more from you than to have the audience rolling their eyes and wishing you'd get over yourself.
Corollary Two to this rule: If you think you're the most prominent person on the panel, you probably aren't. I don't think I've ever seen someone who deserved to hog a panel or who could get away with hogging a panel actually do so. The panel hogs are almost always first-time authors, people who've had a few e-books published or people who've sold a few short stories and who think that makes them special.
In reality, panel dynamics will vary. It's up to the moderator to make sure everyone gets a chance to speak, but there will be quiet people who have little to say and people who are on a panel about their absolute favorite thing who have more to say and who are capable of being interesting while doing so. Just don't interrupt other people, don't jump in on someone else's question or turn talking until they're done, no matter how important whatever you have to say may be, and stop talking when the moderator jumps in with something to the effect of "I'd like to hear what this other person has to say about this." That's the panel equivalent of the Oscar ceremony orchestra raising the volume and it means that it's time to shut up.
2) On a panel, introduce yourself as briefly as possible while still giving the audience enough context to know who you are and why they should care what you have to say.
This goes back to that Swedish belief that the person who has to brag probably isn't any good. The more you say about yourself in an introduction, the more it looks like you're a nobody who has to give a detailed introduction before anyone will know who you are. Larry Niven can get away with introducing himself on a panel as "I'm Larry," and most of us can't do that. But reciting your entire bio with every accolade you've ever received only makes you look like you're either very pleased with yourself or very insecure. Leave that in your bio in the program book, and if people are interested in it, they'll find it. I generally stick with saying what I'm most known for, my latest book and, if applicable, any particular reason that I might be on that panel.
3) You have to share space as well as time on panels or multi-author readings.
It's pretty common to put a couple of books or book covers on the table in front of you so that people can see what you write. Just remember that each person on the panel should get a similar amount of space. Clipping your book cover posters all over the table, building a fortress of books around you on the table or having a mile-high stack of books that partially obscures the person sitting next to you or keeps that person from being able to show a book even spine-out is greedy and selfish. I've heard different schools of thought as to whether or not it's bad to stand the books upright. On the one hand, there are those who say it creates a barrier and on the other there are those who say it's pointless to have the books out without showing the cover. I'd say just don't hide behind the books or infringe on other people's space. If people can't see your face, lay the books down, and limit it to your most recent or maybe the one you're most famous for instead of a copy of every single thing in print that has your name in it.
4) If you're doing a reading, prepare for it.
Very few cons do single-author readings these days, except for the big names, but your schedule sent to you as a guest may not tell you who you're sharing your reading with. Always check before the con on the posted schedule to see who else is in your reading slot. Subtract about five to ten minutes from the overall time in the slot, divide that time by the number of people who are reading, then prepare something to read that fits into that amount of time. Print it out, mark it or otherwise do something to make it easy for you to find right away. Don't get to the reading and then leaf through your book to find your selection or spend part of your reading time playing "I know it's in here somewhere" on your laptop or PDA. Don't take more than your share of time so that someone else gets cut off or cut out.
5) Talk to people.
This one is hard to put into a hard-and-fast rule because personalities and convention dynamics do vary, but you're not going to get a lot of promotional value out of your attendance at a convention if you hide in your hotel room the whole time when you're not on panels or only associate with your friends. The whole idea is to meet people. However, the more time you spend on the convention circuit, the blurrier the line between "hanging out with your friends" and "mingling with the fans" becomes. You may also find yourself in particular comfort (or even safety) situations where you need a buffer zone of trusted friends because someone of the opposite sex has mistaken your general guest author friendliness for romantic interest or because you've picked up a stalker who thinks you are the ticket to his future publishing success and who wants to tell you in excruciating detail about his 1,000 page fantasy epic so you can recommend it to your editor or agent. I probably cling more to my friends than I used to because I've made more friends among the regional con crowd and this is my chance to catch up with them and because I do quite often pick up the unwelcome romantic interest and having friends around allows me to be distantly friendly without landing in an uncomfortable one-on-one situation. Whether you're doing so alone or with a few trusted friends, try to spend at least some time at every con in the con suite or lobby and try to make the rounds of the room parties. It's fine to network with other authors or publishing professionals, and one of the perks of being an author guest is the chance to hang out with bigger names as a professional peer, but try not to get too cliquish or snooty about it, like you're too good to associate with the nobodies. You still need to be available to the fans. On the flip side, it is okay to take time out occasionally to recharge, so if you're a raging introvert and need an hour of alone time so you can be at your best for socializing at evening parties, you should probably give yourself that time.
6) Have something to hand out and put on the freebie table.
Even if someone is blown away by your wit and intelligence, they may have trouble remembering which person of interest you were in the blur of a convention. It's good to have something to leave with people you meet. The old stand-by of a bookmark listing your books works, as do fliers and postcards. If you want something fancier, you can do other giveaways like pens, keychains, coasters, etc. So far, I've just gone with bookmarks. I can leave them on the freebie table for people to pick up and I can hand them out like business cards if someone I'm talking to asks what I write.
7) Remember that your appearance is part of your "brand" as an author, whether or not you put any thought into it (so you may as well put some thought into it).
You don't have to go for the full-on professional attire at a convention, but you do need to be aware that your appearance will leave an impression on people. I think what's appropriate varies depending on the nature of the con, the people who are attending and the specific event. You might not want to wear your Klingon costume or your elaborate fairy outfit when you're on a panel -- especially if that panel includes an editor you'd like to have think of you as a professional -- but you'd probably score points with some of the fans if you participated in a masquerade or costume contest. Most authors don't wear costumes for panels or programming, unless the costumes are related to or part of the programming. There aren't really any fashion rules (beyond public decency laws) for conventions, so costume-like elements often make their way into non-costume attire, and some authors wear things at conventions that they might not wear in their ordinary lives. I think it's probably going to leave a better impression if you're not too obviously "HEY! LOOK AT ME!" when participating in programming -- the visual equivalent of avoiding being a panel hog. Meanwhile, you probably don't want to come to a panel looking like you spent all night in the gaming room (even if you did). Personal hygiene is your friend.
8) Stick to the schedule.
This should go without saying, but apparently it doesn't. If you have been scheduled for something at the convention, you need to be there. If something comes up that will keep you from being there, let the convention staff know as soon as possible. It's also probably a good idea to let your panel moderator know directly if you're not going to make a panel so the panel won't be sitting around waiting for you to show up before they start. Stick to your appointed time so you don't run over into anyone else's time. That includes autograph sessions, and that includes set-up and tear-down time if you do an elaborate display for an autographing. The next person on the schedule should be able to sit down and start signing at the very beginning of his/her signing time, which means your stuff needs to be cleared out by then. Failing to follow this rule is rude to not only the next author, but also to that author's fans, who may be waiting for the start of that autograph session. And, let's face it, unless you're the big-name guest of honor who has a long line, you're probably not going to stay busy the whole hour, and anyone who's going to come see you will likely have done so by the time you reach the 50-minute mark.