Twilight Imperium, 3rd Editionis a massive game. Playing it takes the better part of a day (well-spent, if you ask me), and as such, it is not something you can undertake lightly.
Over the holidays, I put together a Twilight Imperium game at my house, and I thought I would share some tips for preparation and organizing your own game.
You need at least 5 players. No, really. The game is not fun with less than five, because the alliances could form too easily, and the bigger maps can't be used. I think the game works best with 6 or 8 players (but you can only do more than 6 if you have the expansion).
Make sure that there is enough room for everyone. This means a large table, enough chairs for everyone, and possibly some smaller tables for people to organize their bits on (I like TV trays for this).
Despite what the box says, TI3 takes more than 4 hours to play. Typically, for an 6-player game, it's going to be at least 5 or 6 hours, and 8 players bring that closer to 8 hours.
Unless you and your friends have a lot of downtime regularly (for example, you are in college), you will need to set a date a few weeks in advance. Since you are going to have to start pretty early and eat up most of a day, your friends' schedules will matter in planning, so give everyone time to come together for this.
Have everyone bring cash. I like to start before lunch and go up until dinner (at least). This usually means that everyone will need to eat at least once, possibly takeout, and cash is a good thing to make this go easier.
Have a large table and lots of chairs.
The most important rule: make sure everyone has read the rules before coming. Nothing will make the game take longer than having to have a long rules exposition at the beginning of the game, and constant questions during it. The rules are long (about 44 pages for the base game), so this is a non-trivial, but necessary requirement.
Explain the Imperial–Initiative tick–tock unwritten "rule." If you have never played TI3 before, this may be new to you: whoever chooses the strategy card first should always pick the Imperial (8) card, since it gives 2 victory points and gets the game closer to victory. The next person should always pick the Initiative (1) card so that they can pick the Imperial card next time.
If not everyone understands this, then someone will run away with the game as soon as they figure out that the Imperial card is overpowered. Nothing is less fun than being 2 hours into a 6-hour game and noticing that there is no way for anyone to catch up with one of the players because someone let them draw the Imperial card twice in a row.
A possible alternative to this is to use the Imperial II card (in the expansion) with the Age of Empires option.
Minimize the number of optional rules and expansion pieces if you have new players. The game is complicated enough to learn as it is. Specifically, with new players, I don't play with Distant Suns, Leaders, Artifacts, Space Mines, Facilities, or Shock Troops. I will play with the expansion races and cards, but I try to make the first game with people as straightforward as possible.
Many of these ideas can be adapted to other long-running games, such as Diplomacy. Does anyone else have any tips or suggestions for organizing or running a large game?