I'm not gonna lie - sometimes LARP (live action role playing) is like high school, but in character. When you show up on the first day, you have to figure out how you fit in and try not to look like an idiot. In real life, we've all made the decision to hang out with the wrong group of friends or went with a less-than-fulfilling job option at least once.
Those are pitfalls of real life; LARP gives you the opportunity to avoid those things if you wish.
Don't rush a decision. The last time I brought a character in as a PC at a LARP, her personality was already fairly established (because she had been an NPC and I'd played her often). I had a whole plan for her, especially since she already knew everyone in town. She'd hang out with this set of people, join that religion and probably go with the associated kingdom.
Because of in-game events, she was unable to pursue those goals as early as I'd originally hoped. But then all of this other influential stuff happened, and she went on a completely different path. And really, that's the fun in LARPing - it's partially reactive. I'm glad I didn't force the character into a specific path or get too upset when things didn't go the way I had planned. Not planning was more fun!
Let others 'court' you and help you decide. In many games, PCs and NPCs are part of various power groups. These could be guilds, kingdoms, class-based groups or even religious collectives. If your character doesn't have a definite path, why not let others 'court' him? Ask around about the benefits of joining certain groups and why you should join them. This will facilitate role play.
Consider occupying more than one niche. At first it might seem like a good idea to be identified as 'THE healer' or 'THE lady with the big shield,' but over time, you and your character will want to be seen as more than that. Think about pursuing multiple paths. This may also make you more valuable depending on the setting, and it will allow you to fit in with multiple cliques.
Safety in numbers. If you'd prefer to come into the game with an established niche, think about rolling in with a group. Your group should all share one thing in common, even if the characters are all different. Maybe you all share the same trade or all use magic - or it could be as simple as being from the same place.
Leave room to change or expand. One of the most rewarding things about LARPing - whether you're there for a one-shot or a years-long campaign - is the ability for a character to branch out, come of age or grow.