Instructions
Pick the right room. Nothing is worse than going into someone's game room and realizing that it is much too small to really do anything in. Ideally, you want a room that is on the ground floor or the basement, as you won't want to worry about people underneath constantly hearing footsteps from above. Visualize the room and where you are going to put your various games, whether it's billiards, darts, or video games. Use a tape measure to make sure you have room for your games before you order them.
Lay down a carpet. This will help insulate the room and keep the sound from echoing to different parts of the house. Also, it will allow people using the room not to have to wear socks or shoes while playing.
Place the billiards table far enough away from walls. Most game rooms have tables for billiards, but the biggest mistake some people make is putting the table too close to the wall to try to fit more games into the room. Doing this causes every game of billiards to be a hassle. Make sure a person using a billiard cue has enough room to back up nearly as much as they want when shooting.
Mark a line in the ground for darts. Many people just set up a dart board and then figure out an imaginary line to throw from whenever they play. Instead, measure off the regulation distance (7 feet, 9 1/4 inches) and lay down a piece of duct tape or other mark on the ground. This will speed up any future games.
Angle the TV toward the center of the room. Unless you have a designated part of the game room as the "TV section" (with couches, video games, and tables), most of the people using the game room will only be watching the television while they are playing other games. If possible, place the TV on some kind of swivel mechanism so you can rotate it, depending on the game you are playing.
Get the lighting right. You want the regular room lighting to be slightly darker while the lighting above the various games should be spotlighted. Think about how a bar lights their games: They are generally dark places but have intense light over the pool tables and dart boards. This is so people playing have a better view of the board on which they are playing.
Decorate it with your favorite memorabilia. This is your chance to show off your favorite team, school, or state allegiances. Since you are the owner of the room, decorate it however you want. Feel free to post various ticket stubs, posters of your favorite teams, autographs from your favorite players, and anything else you want. Most people like to keep a sports theme to the game room, but there's no rules set in stone for this except that it should be fun.