Moore explained that she rehearsed with Gosling and Stone separately for six weeks before calling them in to train together.
"I would work with Emma in the morning because she is a morning person," she revealed. "She loves to work in the morning and be in early, at 8 o'clock, and Ryan loves to have his day and come later. So I would meet with him at 8 o'clock at night and [we'd] work for about two hours."
"He's very hard on himself," she said of the Canadian actor. "That happens to me a lot as a choreographer. It's if you learn something immediately, the person is like, 'I'm terrible,' and then, 'What am I gonna do?'"
As for Stone? "She has a sweating thing," Moore joked. "She always laughs, she is like, 'I have a sweating thing, I am sweating and Ryan is sweating on me, it is a whole thing.'"
That may explain why the first few rehearsals were, according to Moore, filled with "a lot of giggles."
"And a lot of feeling like, 'Ugh, I cannot get this,'" she added. "There was definitely that initial nervousness."
Luckily, Moore had no problem helping them overcome their nerves, thanks to her longtime experience of working with new talent. Prior to landing the La La Land choreography gig, the St. Louis, Missouri, native was best known for creating some of the most memorable dances on seasons 3-13 of So You Think You Can Dance, a few pieces that even earned her multiple Emmy nominations.
She's worked with almost every one of the show's standout dancers, including fan favorite Allison Holker and fellow Dancing With the Stars pros Chelsie Hightower, Jenna Johnson and Lindsay Arnold, Kathryn McCormick, who later went on star as the lead in Step Up: Revolution opposite Ryan Guzman, and Kent Boyd and Mollee Gray, who were both featured dancers in Disney's Teen Beach Movie and Teen Beach 2.
"I can't say enough about Mandy Moore," Gosling gushed. "She was just an unstoppable force of goodwill that just, I mean, I shudder at the thought of her not being a part of this [event]. She's such a key ingredient to the way it turned out."
"She's the most incredible, patient, brave, and amazing woman," added Stone, "and that honestly was my favorite part of the whole experience -- was getting to dance with her."
La La Land has already made history this awards season, sweeping all seven of their wins at the Golden Globes in January. The Damien Chazelle-directed musical is expected to win big again on Feb. 26 at the 89th Annual Academy Awards, as the movie leads with 14 Oscar nominations.