It is very important that you take the time to read up on the races, their cultures, the existing character bios and different elements of the wiki. The in-game stories are fantastic reads too. Why? Because you are making a character and jumping into a living and breathing world with existing cultures, stories, and people. How do you intend to role play with them and know how your character would act/react to things if you have no idea what the world is about? Also, we have rejected a lot of stories because they tried to create new things in our game world that did not fit our style or existing story. They clashed and were rejected or went through heavy revision.
Playing a PC in our LARP is very rewarding and being able to build your own story and interact with other players is very fun. If you take the time to create a good background and make it believable, it will give you more of a base to role play from and to build on.