Portray a stereotype. Reality TV loves stereotypes, so be a dumb blonde, a ****, a backstabber or maybe a nerd.
Be controversial. No one wants to watch you if you're boring, so spice it up by picking fights with everyone you come in contact with. It doesn't matter what you fight about, just be a jerk. Then when confronted, cry. That way, people will feel sorry for you and want to keep you around longer.
Have a strategy. You want to become an important part of the show's plot, so don't get whisked away early on in the series. Make friends in the beginning and form alliances, then when people start to trust you, turn on them. That makes for good reality TV.
Give a good back story. Nobody cares about the girl next door who grew up in the suburbs with loving parents; we want to root for the poor girl who had to grow up in foster care and work her way to fame and fortune. So be poor, beaten and illiterate.
Sleep with someone. America loves reality TV-star romances, so strike up a romance with a fellow cast member or maybe even the host. When the show ends, let the tabloids see you locking lips with as many famous people as you can find. When all else fails, "leak" a sex tape to the media; that will buy you a few more minutes in the spotlight.
Develop a skill. Whether the reality show requires it or not, you need to be good at something in order to keep your reality TV fame going after the show is over. So learn to sing, dance or write. Standing in one place without falling over could lead to a career in modeling.