The 25-year-old actress was unveiled to the public last week and will debut on the sci-fi drama this Christmas.
"I have an idea of the story, of the character and of a few surprises," she told the Radio Times. "But I don't know her name or where she's from.
"I just told Steven [Moffat] and [executive producer] Caroline Skinner, 'Don't tell me anything until I need to know it'."
Doctor Who star Matt Smith recently praised Coleman, claiming that she gave the "most interesting" audition in front of showrunner Moffat.
"Normally you're just reading in front of a camera, but with this, it was so physical," recalled the actress. "We were using props and running around so it felt like playing - and like a partnership straight away."
Current companions Karen Gillan (Amy Pond) and Arthur Darvill (Rory Williams) will both exit the sci-fi drama in late 2012. Their final episode will be shot in New York and feature the monstrous Weeping Angels.
Doctor Who will return to BBC One in the autumn.
> Doctor Who exec Steven Moffat: 'New spinoff series unlikely'
Watch the new trailer for Doctor Who's seventh series below: