By Lanford Beard
August 18, 2012 at 07:00 PM EDT
Evans Vestal Ward

The Voice‘s zaniest coach Cee Lo Green is given to rocking jumpsuits that look like they’re made of Muppets and stroking his stuffed cat Purrfect. Does that make him crazy? Possibly. But when Green showed up for a guest stint on Nick’s How to Rock (airing tonight at 8 p.m. ET), he was surprisingly understated, donning a plain black T-shirt and relatively few flashes of bling. “I’m used to seeing him in big, colorful feathers and all these crazy outfits,” laughs the show’s 15-year-old star Cymphonique Miller, “and he was really down-to-earth with his outfits when he came on set.”

Green’s no-nonsense air didn’t end with his ensemble, says Miller. “Whenever I work with an artist or someone from the music industry [who comes] into the acting world, it’s always interesting to see if they memorize lines or take the acting seriously,” she notes, adding happily that Green was “really cool and professional…. He really brought his own flavor to the role.” Green also brought his family, a fact Miller appreciated given her own famous pedigree — she’s the daughter of Master P and sister to the artist formerly known as Lil’ Romeo. Below, Miller dishes on what exactly she is doing on stage with Green, another exciting star cameo to come, and the best advice she got from upcoming X Factor judge Demi Lovato.

Tomorrow’s episode — Rock‘s first one-hour installment — follows reformed mean girl Kacey Simon (Miller) as she and her hip-pop outfit the Gravity 5 crash Green’s concert. The on-screen Green was surprisingly cool with the teen takeover, indulging in a duet to Green’s biggest Gnarls Barkley hit “Crazy” and letting the G5 perform their song “All About Tonight.” The concert was only part of a day of singing and improvving in which the starlet says Green became “like an uncle.”

That’s a huge compliment coming from Miller, who looks to her family for advice and encouragement. When she was doing the rounds as an up-and-coming actress, Romeo — who headlined an eponymous Nick show (also starring his dad) from 2003-2006 — made a point of keeping of her grounded. “He told me, ‘This is going to take a lot of hard work, and you have to pay your dues.’ I was ready to do that because I definitely didn’t want to gain anything off of my brother or dad.” After guest starring on Big Time Rush, True Jackson VP, The Troop, and Just Jordan, Miller scored the lead on How to Rock from an open audition where the casting agents didn’t realize she was related to Romeo. “It was cool that Nickelodeon really believed in me,” says Miller.

Though Miller didn’t appear in Romeo!, she’ll get the chance to act opposite her big bro in an upcoming episode, in which Romeo plays a talent show host. As fun as it was, Miller admits that pretending a family member is a stranger can be pretty confusing. She giggles, “It’s really crazy because, while we were on set and doing lines, one time he accidentally called me by my name, and I’d be calling him by his name. We’d be like, ‘Oh, we’re supposed to act like we don’t know each other!'”

It’s a neat coincidence that one of Miller’s most trusted advisors plays a character involved with a talent show when another of her famous friends was a big help along the path of early stardom. Miller opened for Demi Lovato a couple years back. She says the the Disney vet and soon-to-be X Factor judge “always was really positive and said ‘Be yourself no matter what.” It’s a piece of advice Miller thinks all her fans should take to heart. “Comparison is the enemy of happiness. You have to be the best you,” she says. “Even when people say they look up to me, I’m like, ‘Don’t try to be like me. Be the best you.'”

“How to Rock Cee Lo” airs tonight at 8 p.m. ET.

Read more:

Nickelodeon greenlights spin-off pilots for ‘iCarly,’ ‘Victorious’ from creator Dan Schneider — EXCLUSIVE

More ‘Big Time Rush’ coming to Nick

Nick cancels ‘Victorious’ starring Victoria Justice