Ambiance is something that I've talked about on here before, but for the life of me I can't think of where I did it. It is something that RPGs have a problem with. It is something that almost every other medium for story telling can do better. However, it is also one of the most powerful ways to sell a story or a feeling, and so you can't ignore it, hard as it may be.
I've been, slowly, playing through Space Marine lately. It is a fun game with solid controls, pretty graphics, and a decent story. What gets me the most about the game though is the ambiance. I have yet to feel more powerful in that game than when I showed up to a fight and heard the Imperial Guardsman cheer out "It's a Space Marine! The Emperor's Angels of Death have come to save us!" It wasn't during a cut scene, it wasn't focused on, but I heard it in the background: called out over bolter fire and screaming orks. This feeling was then backed up moments later with the awe-filled whispers from other IG around the area, including an injured trooper saying "At least I got to see a Space Marine before I die, I can take that with me."
The feeling is powerful precisely because it isn't focused on. It is so casual it doesn't need to be focused on. So what could it do in your game? A lot.
The big problem with this though is that everything the GM says does have focus, and so it can be harder to find ambiance in a game. Whatever the GM or a player says gets detailed in that moment, as if the camera focused on it, which makes it a deliberate attempt to do something. That doesn't mean it can't be done, just that it is a bit harder. So, what are some methods?
Soundtracks for your games are possible, but they are also a lot of work. Finding the right music, getting it ready to go, and playing it loud enough to be heard but soft enough to not distract can be one hell of a juggling act. However, do it right and music will carry your game. Some scores just inspire emotions, and music can convey it better than most of us can with words. You want people to feel like an epic adventure is beginning/going on, then play the score from Halo or Lord of the Rings. The scores there just scream out epic, and timed right you can do a lot with it. The same is also true for sadness, happiness, and even dread or revulsion. here is music out there for it, so find it.
One of the ways that I've been trying to do it is in my descriptions. The idea here isn't to focus on it, but just drop the lines casually while describing what is going on. "The injured are aligned along the far wall, whispering amongst themselves with sidelong awe filled glances at your presence. The beds have seen better days and it smells like their bandages haven't been changed any time recently. Beyond them..." it is just done quickly, but it is something that they can catch on to. Do it consistently enough and you will pull the feel you want out.
How About You?
today I'm only giving two ways, but I'm curious what other ways people have found to create ambiance in their games. What do you go for? What have you tried for? What worked/ What didn't? Sound off in the comments.