1) Don't hog the spotlight. Yes it's more fun when you're the focus of attention, but everyone is there to have fun. This includes in game and out of game.
2) Don't rules lawyer/setting lawyer. Unless the GM is making a mistake that will kill a character, wait until after the game to ask about it. You may know something more about a given setting or system than the GM, but you're not the one going to the effort of providing a game for everyone else and having to mentally juggle a zillion things. And half the times I've been called out on rules I've turned out to be right, and usually in the other cases I still stuck by my ruling (the exception being if my mistake would off a character).
3) Don't waste time. Nowadays, everyone's time is valuable and game time may be limited. Don't slow things down by playing with your iPhone, browsing the web or reading instead of paying attention and being ready when your turn comes. Sure what everyone else is doing may not be as interesting as that text message or the latest issue of Captain Thunder, but it's rude to make everyone else wait (and as a GM I personally would be tempted to skip that player's turn).
4) Limit the tangents. Try to keep down the distracting funny comments, smart aleck remarks and side conversations. I'm often guilty of this as well, and it can be hard, but if you only have 3-4 hours to play and lose an hour to banter... that's 25-33% of everyone's game time gone.
5) Don't whine. If the GM was really out to get you, your character would probably be dead already.
6) Don't make "joke" actions. See above about wasting time and an evil GM (we're all evil) may decide your character carries out whatever stupid thing you thought would be funny.
7) Don't harp on the setting or system. Not everyone is going to like every setting equally, and no game system is perfect. But the GM picked those for a reason, and when you run a game you can pick your favorite setting and system. Rubbing the flaws of the current game in the GM's face wins you no points.
8) Don't cheat. I think this should go without saying, but some people have done it in the past and it happens at tables out there. And people will notice if your mech seems to have extra armor points or you snatch up your dice as soon as you roll.
I know this list isn't exhaustive, but it's a good start and probably similar to advice you'll find in other sources. Like I said, as a GM, I'm pretty lucky. Now I need to come up with the GM Etiquette side.