By Lindzi Scharf
March 14, 2013 at 01:00 PM EDT
Ditte Isager/ELLE

You know you’re a powerhouse stylist when one of your most famous clients moonlights as your interior decorator.

Leslie Fremar — who counts Charlize Theron, Reese Witherspoon and Scarlett Johansson among her A-list clients — landed the top spot on The Hollywood Reporter‘s annual list of the 25 Most Powerful Stylists, appearing on the cover of the issue with longtime client Julianne Moore, with whom she shares more than just a passion for fashion. Turns out, Moore is an interior design enthusiast who has helped Fremar decorate her New York City abode… twice.

“Julianne has impeccable taste and decorates her own homes… it’s something that we have bonded over,” explained Fremar. “We do fittings in her house, which is inspirational and beautiful. [One day], I started asking her for advice.”

In 2007, Moore gave Fremar’s then-residence  — a West Village apartment — a floor-to-ceiling makeover for a photo shoot in Domino magazine. When Fremar relocated to a three-bedroom TriBeCa loft in 2012, she took the lead on the design process, but still relied on her star client for guidance. “I brought over a lot of pieces that she’d found for me for my old apartment. It was a larger space, so I needed to get more furniture,” Fremar said. “I trust Julianne’s aesthetic, so it made sense [to get her opinion].”

Though Fremar is the sartorial expert — in addition to styling, she designs a collection of tees and tank tops for Fruit of the Loom and is rumored to be working on a denim line with client Charlize Theron — she knows it never hurts to get a second opinion, especially if it’s from someone like Moore, an interior design hobbyist whose West Village townhouse has been featured in Architectural Digest. “With decorating, it’s very different from styling. Decorating is a larger puzzle,” Fremar explained. “We’re friends, so Julianne comes to my house. Every time she’d walk in, I’d say, ‘Let me just ask you one more thing…’ Or I would e-mail her pictures of things I was looking at on websites.”

She may get star treatment from an Oscar-nominated interior design advisor, but Fremar joked that it’s impossible to forget who the celebrity is. “When we decorated my first apartment, we went to Ikea together,” the stylist remembered. “People were looking at Julianne like, ‘What is she doing in Ikea?!'”

Click on to see Fremar’s best interior design tips and tricks (some of them handed down from Moore): 

Here are Fremar’s top 4 fashion-inspired decorating tips:

1) Know when to spend and when to save. “Julianne is a great person to bounce things off of on where you should spend your money and where you should save it. I’d ask, ‘I need light fixtures—where do I go?’ She likes simple things, so she’d say, “Don’t spend too much money on your fixtures for your hall. Just go to the hardware store and get those generic ceramic light fixtures. Save your money there, so you can end up buying something else.”

2) Finding the right furniture is all about fit. “There’s a lot of things to take into account when purchasing items—like proportion and size. I live in a large loft space—and decorating a loft space is different from decorating a smaller room. You need bigger couches; you need bigger rugs. Some things you find beautiful won’t work. I would find that I would be passionate about something and would love it, but then it would show up and it would feel dwarfed or wouldn’t make sense in the space. You have to evaluate your space and consider the volume of the type of pieces that you need.”

3) Look for vintage finds online. “I buy a lot of stuff on EBay and have it restored or re-upholstered. With furniture, there’s so much you can do to it and there’s so many places you can buy incredible fabrics and have things recovered. If you love something, you can try to figure out a way to make it work.”

4) Don’t get stuck in a rut. “I had an old dress that I used to wear all the time. I loved the fabric. With fashion, you get sick of things much quicker than something in your home. I just really loved this pattern, so I had it made into a pillow. So now it sits on my couch. I can look at it every day, but I don’t have to wear it all the time.”

Read more:

‘The Hollywood Reporter’ names the 25 Most Powerful Stylists of 2013

Hairstylist Mark Townsend on how Jennifer Lawrence’s hair has changed (but she hasn’t)

Matt Damon lost weight ‘to make the clothes fall better’ in HBO’s ‘Behind the Candelabra’ — EXCLUSIVE