Need some advice!? =/?

i was just wondering, how do i become a more outgoing person? ok so i'm really queit expecially around new people or people i don't know that well. i'm loud around my friends but in school i tend to be really quiet and i was wondering if anybody had any advice on how i could be more outgoing. btw what makes me quiet most of the time is that i don't know what to talk about, so i end up thinking about what to talk about too much and not say anything.