The former American Idol panellist - who recently quit the talent show - believes that Spears needs to remain calm and speak "right from the heart" when she is voicing her opinions to contestants in front of a live TV audience.
Speaking to Entertainment Tonight, she said: "There comes a certain type of pressure when you do the live shows, you have to be on every single minute. It's just about being relaxed and being honest and being yourself.
"If you're honest and yourself then you kind of come off as you should. If you try and think too much about what people might think or what you're saying then I think you get lost.
"I always spoke right from the heart and how I would want someone to speak to me if I was in that position which I had been many times, and it worked really well for me and I had a great time."
Mariah Carey has signed up for American Idol as one of the replacements for Lopez and Steven Tyler, who has also departed the show.
The 'Jenny From the Block' singer added that 42-year-old Carey will do a great job on the 12th series as long as she is "herself".
"So long as she's honest and speaks from the heart and is herself then I think she'll be fine," Lopez concluded.
Watch a promo for The X Factor USA below: