How can you be a superstar in DreamLife Superstar

Writer: Sign up for any writing oriented activities
Pop Star: Sign up for "Sing In Band"
Reality TV Star: Anything, a talent scout will come to you at random...This usually happens when you don't do things that fall under another category.
Movie Star: Talk to people and constantly chose, "Let's Do Something!" and pick get a coffee, or let's see a movie when they are available.
Athlete: Sign up for any sport
Fashion Designer: Sign up for any artistic activities

Hope this helps. :)