just be fun. i like making up random crap. she'll obviously ask you the basic questions like where did you grow up, where you're from, what you do etc... so "i'm was born in the arctic, my parents are eskimos", "i now live in a boathouse in the sahara desert", "i'm studying rocket science. i got a bursary from zimbabwe's secret space program" (one girl actually believed that i was studying rocket science

- excellent time to tease the crap out of her)
fun, playful and most importantly - you're different from every other guy she's met.
check out the routines section for some stuff to fall back on. 5 lies game, the cube etc are all pretty good.