‘I’m only mean in the movie!’ Kindness key for Melissa McCarthy

Melissa McCarthy knows how to fix the world.

“When someone is being their authentic self and it hurts no one else in the world … the simplest rule is: Just be kind,” she says.

In a long, white flowery dress on a weekday morning, the 52-year-old native of Plainfield, Illinois, who was raised on a farm, always dishes out the kindness and normalcy.

She will take you back — way back — to when others gave her a little TLC. “I didn’t even know you could be an actress,” she says. “I moved to New York never having been there. I wasn’t even on a plane until I was 19.”

And now she’s describing the premiere of her big summer movie, Disney’s live-action “The Little Mermaid,” opening this weekend. Yes, they shut down Hollywood Boulevard (and painted it blue!) for McCarthy and company.

Her take? “Premieres are a time to bring out your lip and your lash,” McCarthy says of her “fancy” makeup evening. “I know it sounds silly, but I’m still that girl from the middle of Illinois wondering ‘How did I get here?’ ”

Here at a media event in L.A., it’s clear that McCarthy is one of Hollywood’s biggest female comedic performers, with a filmography that includes “Bridesmaids,” “The Boss” and “This Is 40,” plus TV roles in “The Gilmore Girls” and “Mike & Molly.”

It was a no-brainer when Disney reached out for the retelling of “The Little Mermaid.” McCarthy plays the conniving sea witch Ursula, who makes poor Ariel (Halle Bailey) a deal in which she must trade her beautiful voice for human legs so she can live above the water with her true love, Prince Eric (Jonah Hauer-King).

McCarthy’s above-water life includes her long marriage to writer-producer Ben Falcone, their production company On the Day, and their daughters, Vivian and Georgette.

Her good life tips:

Refuse to hear ‘no’

McCarthy figured her odds of becoming an actress with no “foot in the door” were slim. But she didn’t care. “I think if anyone tells you the odds are slim, you just keep walking,” she asserts. “Keep doing. Just do whatever the hell you want to do because how do they know? They don’t know what they’re talking about in many cases. My rule is, if you love something, work really hard at it and see what happens. You can do it.”

Embrace the moment

“You have to collect your thrills,” the actress says. “If you love what you do, it doesn’t matter how many times you’ve done it. It still feels great in that moment.”

Don’t play the blame game

“I’ve never been someone who blames the world for her problems,” she says. “You are your problem; you are also your solution.”

‘A little nervous and excited’

McCarthy acknowledges that she gets anxious before her films are released. “It’s like sending the kids off on the bus on the first day of school,” she says. “You work on this thing that’s such a long labor of love and create something of beauty and then say to world, ‘Here you go. It belongs to you now.’ Yes, you get a little nervous and excited, but you should be both of those things in life.”

Laugh and cry

She admits it: She’s the first one to cry at a movie. “It’s funny because I know every part of ‘Little Mermaid,’ ” McCarthy says, “but when they showed it to me for the first time, I kept saying, ‘Oh God, oh God, this part is coming and I’m going to cry.’ And then it was, ‘Here it is! I’m crying.’ I think it’s quite healthy to laugh and cry.”

Collect your mom thrills

“This movie was the first time my two kids wanted to actually come to a premiere,” McCarthy says of 16-year-old Vivian and 13-year-old Georgette. “They wanted to meet the people, and soon my kids were like, ‘Oh, my God, Halle is right behind us!’ I’m excited when they’re excited.”

Chop things down

Her biggest mom tip? “Navigating each day with my two girls, I hope I’m trailblazing,” McCarthy says. “At least in the sense of chopping things down and making the path for them a little better. … We both just want them to do something they love in life and hopefully just feel good and happy. My girls could be gecko catchers in the Galapagos Islands or they could act because they’re both very artistic. The point is, I just want them to find their joy and lead with kindness.”

Find common ground

“I’ve learned in life that everyone walks with the same troubles and worries,” McCarthy says. “It’s just part of being human. We’re all just out there trying to do our best. You can find common ground with so many if you try.”

Have fun at work

What was the best part of filming “The Little Mermaid”? “Every single minute of it,” the actress says. “Here I was at rehearsal standing on this crazy 60-foot clamshell. Or maybe the best part was me trying not to cry every single time I sang a melody. Quite often, there would be tears running down my face.

“I slipped on that clamshell. Once,” she adds. “The truth was, I was never on my feet. I was up on a rig and diving around in the air. … It was all glorious.”

‘Not today, Ursula!’

McCarthy recently met two little girls who were afraid of her because of her ‘Mermaid’ role. “I tried to get really low and kneeled at their level, but they were so tiny and cute and sure of their feelings. The girls were like, ‘Oh no! Not today, Ursula! I see you and I’m not buying it!’ ” she says. “I was like, ‘Girls, trust me. I’m only mean in the movie!’ ’’