No, I'm not talking about the mixture of gasses and such that we breathe (but you already knew that, didn't you?). I'm talking about what can set a good game apart from a mediocre one. Sometimes, it's those little touches that make things truly memorable, provided they're chosen well. What follows is a sort of primer on how to create atmosphere in Role-playing, from music to props to food (depending on how elaborate you and your players want to get!).
1. PROPS. Usually, you hear more about the use of props in Live-Action Roleplaying, but they can often be used to liven up a tabletop game, too. They don't have to be elaborate; something as simple as a hastily-penned note from as NPC can serve as well as a professionally-drawn map.
If you want to get a little more involved, try using actual objects carried or worn by NPCs. One of my Toreador vampire NPCs (in the eponymously named RPG, natch) wears a crescent moon necklace, and I discovered that playing her became a bit easier after I found one to wear myself, in-game. It also served as a very useful piece of evidence after that same character had been kidnapped by the evil Sabbat (after one of the PCs used Psychometry on it to determine her location).
Other things can serve as props, too; just let your imagination get to work on objects you can find around the house. For example, a very pretty "blank book" that I received as a present made a marvelous spellbook for a fantasy game I participated in while in college.
Don't neglect old toys, either. One of my old Barbie dolls has been given a new lease on life (or should that be unlife?) as the plaything of a ten year-old Malkavian vampire in my World of Darkness games. And a toy crossbow (after a coat of paint and some detailing) served me very well as "Nightstalker," one of my superhero PCs from Dark Champions.
2. MUSIC AND SOUND EFFECTS: If chosen correctly, these can really get your players into the game. For example, with a little help from my friends, I've put together a tape of vampire-themed music that we play whenever the PCs are in the local vampire bar. And a tape of "new age" music by the group Geodesium did wonders to evoke the atmosphere of an occult bookstore run by one of my mage NPCs.
For fantasy games, any number of fantasy-based "filk" songs can add a little "local color" as songs performed by a wandering minstrel in a tavern, or perhaps even by one of the PCs themselves. I recommend any of the collections based on the "Valdemar" series by Mercedes Lackey, which capture the flavor of high fantasy quite well.
(Nota bene: A bit of explanation may be in order here. For the uninitiated, "filk" music refers to folk music based on some aspect of science- or fantasy fiction. A number of fine collections by artists such as Heather Alexander, Leslie Fish, and Tom Smith can be obtained by mail order through companies such as Firebird Arts and Music; they often advertise in science and fantasy fiction books and catalogs. Give them a try, but be warned -- these tapes can often prove to be addictive.)
If you're looking for sound effects tapes, try costume stores, or larger drugstores and card shops right around Halloween time; tapes of "spooky" sound effects can often be obtained for minimal cost. The next time your PCs hear the creaking of a dungeon door, or the maniacal laughter your villain, you can actually let them hear it, rather than just relying on your description. Don't be surprised if you get a few shudders out of some of them, especially if they aren't expecting it!
3. FOOD. Okay, I realize that I'm getting a wee bit more elaborate here, but isn't it time you got out of the fast food rut anyway?
All kidding aside, though, sometimes the judicious use of edibles will really add to the atmosphere of a game. I fondly remember the plethora of red (and only red, mind you) beverages that was served at a Vampire game I GMed. Somehow, sipping cherry pop from a wineglass, rather than my usual Coke from a paper cup, really helped capture the feel of The Vampire Lestat, the Kindred nightclub owned by my Toreador Primogen.
If you're lucky enough to have one or more players who are willing to contribute their own culinary talents, by all means tap them as a resource. After all, the aid of more people will help if you want to get more elaborate. How about a medieval feast for one session of your fantasy game? Your only limit is your imagination (and how far you are willing to go)!
That's all for now. I hope that I've gotten your creative juices flowing, dear reader, and wish you the best of luck in your game! See you next time!