Table rules: how do you keep your players focused on the game?
I'm going to take a page from Lindevi here and provide a top 5 list:
Table Rule #1: Come prepared.
I don't mind letting people borrow my dice at convention games or the like, but when you're coming to a regular campaign, you should have your own supplies. This goes for everything you need--your character sheet, your dice, your pen or pencil, any books that you require. When a player shows up without their basic gaming kit, the entire table suffers.
Table Rule #2: Keep the whole game moving.
When you've got the spotlight, it's easy to want to dance. When the story is centered on your character, it becomes easy to monopolize others' time, including your GM's. However, for every sidebar or storyline that you take the GM away from the table, the rest of the gamers at that table are left hanging in the wind. There's nothing wrong with individual character vignettes, but be judicious and be fair in how much time you're taking from everyone else.
Table Rule #3: If someone is offended, then it's offensive.
|Seriously. Follow this one rule and|
you'll be fine at any game table.
Table Rule #4: Be on time.
Pretty simple, this one, but it's another thing that we've had issues with in the past. When there are several other people waiting on you, it's only courtesy to ensure that they're not waiting long.
And lastly, the most important rule: Don't be a dick.
Even Wil Wheaton says so!