Jag hoppas det går bra om jag skriver på engelska:
Here are a few tips I try to use to build atmosphere in my games of Call of Cthulhu. Start with a quiet room where you won't be disturbed. Don't leave anything distracting lying around. Play after dark, or draw the curtains. Have candles ready, so that when night falls, or the characters go into a cave, basement etc. you can light the candles. Darkness and flickering shadows really work!
Appropriate music is a must, but don't play it too loudly, or it will just distract everybody. I prefer to use horror soundtracks, or classical music. Avoid rock music of all kinds unless your game is set in modern times. The main problem with classical music is that it usually tries to evoke several different moods, not only fear. This is also true of soundtrack music. The solution to this is to either programme your CD player, or make tapes of the pieces of music which fit best with the mood you want to build. Have one tape of eery, suspense-building music, another of exciting combat music, a third of 20s jazz for the speakeasy scene, and a fourth of completely weird music for when the characters go through the gate to Yuggoth. Important NPCs can be given theme tunes, to help the players recognise them. Play the tune whenever that NPC appears. Lots of ideas can be found at: http://www.eerie.fr/~alquier/HPL/music_list.html.
You can also use sound effects. I once ran a game set in a haunted house during a thunderstorm, and played a CD of a thunderstorm continually in the background, with no other music. It worked a treat. Ethnic music can also work well - I once played a game set in the Australian bush, using aboriginal digeridoo music at appropriate points, which worked well.
You can also play up your characterisation of NPCs. Use the space around the gaming table - get up and walk around. Stand behind the players. Be physical. Invade their personal space. Touch them. Talk in their faces. Refuse to respond to their jokes. Vary your tone of voice, too. Talk in a whisper when things get creepy - shout when things get violent.
However,be careful not to overdo it - I don't recommend you do this for an entire gaming session, only when you're trying to build mood at the scary bits. Remember you're doing this for fun, and try to get the players to agree to get into the mood. You can't do this for hours on end, so just play as normal until the bad shit starts happening, then put on the scary music and start trying to creep the players out. Humour is an important part of horror - it's natural to respond to fear or a shock with laughter - so try to create fear in waves. Start with a small shock, then relax, then hit them with something bigger, then relax again, then build up to something really awful. Horror movies do this all the time - the key is the drop in tension between scares.
Sometimes you'll get a player who appears to be deliberately trying to destroy the mood that he knows you're trying to create. Here's a good article on how to handle players who do this:
http://www.johntynes.com/rl_mofo.html.
Another good technique is to physically isolate the players.
When the party splits up, take the players who went off on their own aside and deal with them separately. Don't let on to the main group what's happened to them.
Have fun!
