First things first
Follow Barbara Mawdsley (M). She'll tell you what you need to do and where to go.
Next steps
Study the terrain. There's a map of the area here
Come to the Royal Festival Hall on Saturday August 1st between 11am and 4pm. There will be a mission control centre in the Clore Ballroom. Barbara Mawdsley will have already told you what to do - if not, come and ask.
What to bring
You'll need a cameraphone/smartphone with a mobile internet connection. Don't always trust the WiFi... someone may be watching the network. You'll obviously need a Twitter account. Your phone will need to have access to Twitter and be able to send pictures to a service like Twitpic
How to perform your missions
Barbara Mawdsley will send you direct messages (DMs) on Twitter, that no one else can see. These will contain instructions on what you have to do.
Sometimes those instructions will be in the form of links to pages on the Internet containing maps and photos. If you're asked to photograph something, take a picture and DM the Twitpic link to Barbara Mawdsley. If you're told to send back a word to complete a mission then DM just that word to Barbara Mawdsley.
Want to tell people what you're doing?
If you want to talk about the game on the day, use the hashtag #qntmfslc. Please don't include any spoilers though.