Author Gaiman wrote series six episode 'The Doctor's Wife', which went on to win the 2011 Ray Bradbury Award for 'Outstanding Dramatic Presentation' and the 2012 Hugo Award for 'Best Dramatic Presentation, Short Form'.
Asked if Gaiman's series seven script was linked to his previous effort , Smith told Digital Spy and other reporters at London's MCM Expo Comic Con: "No, it's very different.
"But again I think it will be a fan's favourite because, well, without giving anything away, it just will be, because there's something in it.
"Neil's brilliant ideas will always add a level to Doctor Who, which will be interesting."
Of Mark Gatiss's return to the show, he added: "Mark, wonderful writer, wonderful actor, wonderful friend, wonderful man, he is literally the nicest man on the planet, Mark Gatiss.
"He's just a dream to work with and he really understands the show. He gets it, he gets the Doctor, and you're always in good hands with him.
"You've got Diana Rigg, who's fantastic, in his episode. We always have high ambitions."
Asked about working with Richard E. Grant on the show, Smith said: "He's such a pro and such a brilliant villainous actor as well and I'm a huge fan of his.
"For our generation you watch Withnail [And I], and that defines so much for all of us as a film. He very kindly did an impression, 'Booze. I must have booze! Give me booze!'.
"He's just a wonderful, kind, clever, brilliant actor. He's got a lovely spirit and nature and I think he's perfect for Doctor Who."
Grant's appearance is his first canonical Doctor Who performance after his voice work on animated webcast 'Scream of the Shalka' and appearance in Steven Moffat's comic sketch Doctor Who and the Curse of Fatal Death
Doctor Who: Series 7: Part One is available now.