The swimsuit model – who is currently filming Just Go For It with Aniston in Hawaii – told ET Online that her castmate has been "encouraging" during her big screen debut.
"She gives me tips here and there... She is stunning. If you can have somebody who is as beautiful as she is and as kind as she is, it's just such a great mix," she explained.
"The most surprising and amazing thing about her is she treats everyone like she's been best friends with them for years. The first time we met, she came up to me and said, 'Hi!' and opened her arms and gave me a big hug and said, 'Nice to meet you!'"
The Sports Illustrated cover star – who is married to Andy Roddick – went on to say: "She's been like that the whole way. Someone in her position doesn’t have to be that way and she is. It's incredibly refreshing."
Decker added that the entire cast – which includes Adam Sandler and Nicole Kidman – are "absolutely amazing" and "the best people to work with" on a first project.
Just Go For It is released next year.