"When I meet young girls, I'm always like, 'Just do me one favor,' " she tells PEOPLE in its new issue. "Love what you look like right now – and remember I said it 10 years from now because it's the greatest gift I can give."
Having already witnessed first-hand how tough it can be to love your own figure – the 31-year-old spoke out against critics in December 2007 when unflattering photos of her on the beach surfaced – Hewitt says she first focused on getting a mind makeover.
"I just really worked on my mental part for a couple of weeks, got myself in a really good mindset," she says, adding that she was "bummed out" and "had to get over the embarrassment of the photos.
Then, the Ghost Whisperer star decided to give up her beloved donuts and make time to squeeze in workouts during her busy schedule – to get healthier, but not slim down drastically.
"I think I'm a work in progress," she admits. "[But] I feel it's so much better than [it was] a year-and-a-half ago, and I feel like in another eight months, it's going to be so much better than it is today."
Even with her new-found confidence, the 5-foot-2-inch Hewitt, whose Lifetime movie The Client List airs July 19, still fesses up to dreaming about having a certain body type.
"I'd want to have Gisele Bundchen's body. Even though she's tall and skinny, she does have curves … and I think that's hot," says Hewitt. "Halle Berry also is kind of amazing."
For more on Jennifer Love Hewitt – including her diet tricks, exercise secrets and (honest!) thoughts on plastic surgery – pick up this week's PEOPLE, on newsstands Friday