"I used constructive criticism. I learned from the best," the pop star, 30, says, pointing to fellow judge Cowell during an interview airing Tuesday on The Ellen DeGeneres Show.
"I prefer to be honest. I think that's the best way to go," she adds. "I wouldn't want to be told something and then waste seven years of my life. I feel like it's the thing to do."
"I'm not disagreeing with you. I've been doing it for years," replies Cowell, 52, though he did reiterate something he said about Spears on a recent conference call: "I've never heard someone say no [to contestants] so quickly in my entire life."
Though she may be a merciless judge, Spears admits to having her own butterflies at first. "I was really nervous," she says of starting her gig on the show, which premieres its second season on Wednesday night (8 p.m. ET, Fox). "You have all these people behind you, and you know they're rooting you on. It's a really exciting, electric thing to do."
As for who will succeed Steve Jones as host for season 2, premiering Wednesday night on Fox, Cowell said Khloé Kardashian is certainly among the favorites, though he still needs approval from Fox.
"It could be a Kardashian. I think that would work," he says. "We have to find people who have a great chemistry, but Khloé is definitely up there in running."
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