Since there seems to be plenty of us LARPers here, let's share. Let's try to keep the actual tricks short and then expand by Q&A, if convinient.
Pre-written characters are a norm in our games. LARP's are tricky beasts when it comes to controlling what actually happens in the game; GM guidance during the game causes all kind of havoc during the event. Unlike tabletop play, LARP's don't have a single point of focus for information, since players are spread out in larger area (from a single room to a whole city) and usually the metagame level is non-existent. Stopping the in-game for few players to negotiate and clear things out does not mean it stops for other players, among other things.
So we like to do pre-written characters for several reasons:
- Consistency. We can make sure that all characters have consistent information about the setting, other characters, goals and possible plots. Inconsistendy can be added by design and choice and that too is, well, consistent (for example, characters have different information about something that has happened).
- Cut out the need for adding new content (as in setting content) during the actual play. LARP's are not good medium for improvising setting content during the play because of their decentralized nature. If someone introduces new elements to the setting, how do you inform other players about it? Small details are a different matter.
- Plot control. Controlling the plot/events/storyline/whatever during the actual play is troublesome. While it could be done with use of NPC's, GM control, or other means, we like to use the pre-written character since it's a most likely way to exclude the need of control during the actual play. You can insert all sorts of parameters, hooks, goals, plots and stuff to a pre-written character.
- Social networks and character contacts. With pre-written characters you can design a web of connections between the characters and add a lot of stuff that can turn into situtations and player-driven events during the game.
The use of pre-written characters and front-load designing could be condensed to this: you prepare the table for the players, give ingredients and tools, which they can use in whatever way they choose to. You prepare a lot of possible situtations. Then cut off the control and see what happens.
Edited: fixed the header.