- Be Prepared - Know what you are responsible for and what you need to have with you. If you are sitting down to a game and you weren't told that dice will be provided, then have a set of dice valid for the game on hand. If characters are pre-genned, have your character ready to go or work out with the GM ahead of time when you will make one. As a player you are responsible for being at a game on time and ready to go, so be prepared.
- Ask Before Taking - Do not look at another gamer's character sheet without permission. Even if they gave it to you before, ask before looking a second time. Don't touch another person's dice without explicit permission. Seriously, some people are very personal about these things. Others don't care. You don't want to risk causing an awkward situation because you 'borrowed a d10' from someone who subscribes to the "you touch my dice, I slit your throat" rule of personal possessions. An extreme example, sure, but a lot of gamers take very personal umbrage if you mess with their stuff without permission.
- It's Not Worth Arguing - Even if you know you're right. If it is a new game, or at a con, then don't argue with the GM. Arguing just bogs everything down and removes fun. Instead, go with the flow. If you don't like how the GM rules, then don't sit at their table again (it is new, after all.) Go with the flow, have fun, and let the GM rule as they need to to keep things going. This is especially true in Con games where GMs only have about 3.5 hours to run a whole adventure, often while having to explain basic combat mechanics to people who are just trying out the game.
- Pay Attention - New games and Con Games have you in a constant state of making first impressions. People may understand if you are dead tired and zonk out at a 2 am game at a con. They're less likely to be thrilled if you constantly have to have the situation explained to you again and again. Remember, time is fun in gaming and the more people have to repeat themselves, the harder it is to get through things.
- Share The Spotlight - Often table top games have screen time gated by the number of people in a scene. This is even more important in convention games where time is at a premium. Share the spotlight. Don't be so fixated on getting your crowning moment of awesome that you kill someone else's. Be courteous. You'll get your chance, and if not, oh well. It's just a short game, and the people you let have their moment are more likely to be willing to help you get one now that they've seen you're not playing selfishly.
And that is it for me. Do you have other advice for basic etiquette? I laid off the personal stuff like hygiene for a reason, but just remember good hygiene is always important.