"We talked a lot beforehand, so we had it figured out what we were going to do, what bits are we going to feel, and what bits are we not going to feel," McAvoy, 28, told PEOPLE at the Chanel and Cinema Society premiere of the 1930s period drama, held Monday in New York.
Any tips for doing a sex scene? "Breath mints," he advises. "Don't have a lot of garlic. Don't have a salmon-and-cucumber sandwich beforehand."
He also suggested that there was choreography at work during his steamy scene with Knightley, something the two of them had worked out in advance.
"What we do first and what happens next," said McAvoy, who previously was seen as the goat-like Mr. Tumnus in The Chronicles of Narnia and the tortured Dr. Nicholas Garrigan in The Last King of Scotland. "We tell a story. There is an emotional journey shooting the sexy scene, so it's not just, 'Alabalabalaba.' "
Mum on MarriageAs for his wife, actress Anne-Marie Duff, whom he met in 2004, when they both appeared in the British TV show Shameless, they live in London, have no children – and he doesn't discuss their relationship, reports The Washington Post.
"We don't talk about each other much," he tells the paper, "and we don't turn up together at lots of events. We both really rejoice in having a normal life."
Sure enough, when asked by PEOPLE how the two celebrated their first wedding anniversary on Oct. 18, McAvoy replied, "I'm not telling ya."