Tom, who plays Draco Malfoy, said it's good to make the casting people laugh, as they'll stick in their minds.
"If you can make them remember you, then it helps. Obviously being a good actor helps too!"
Thousands of girls are expected to turn out in the cold for the open auditions being held in London tomorrow between 10 am and 3 pm at Pineapple Studios, 7 Langley Street, London WC2.
Tom also added a few words about filming the third movie.
"There's a new director and new cast members, which is always a good laugh because they always fit in perfectly. There's some location shooting in Scotland and new places I've never been to before so it's been a good laugh, an all-round good experience."