Ruiz was sensationally crowned IBF, WBA and WBO world heavyweight champion by stopping Joshua at Madison Square Garden at the start of this month.
The Mexican is set to face Joshua in a rematch later this year and says the 2012 Olympic champion does not have the skills to reclaim his belts.
Ruiz said: "The rematch is going to be the same. I am going to be more prepared and more ready.
"I know his flaws. I can do a lot better. The only thing that he can do is just run around, he's not good at boxing."
The rotund Ruiz added that he will be in better shape when they do battle for a second time.
"People thought I wasn't going to do anything, I was too big, too overweight. I don't want to say all the things I am going to change," the 29-year-old said.
"There is going to be a lot of changing, I am going to come at a better weight this time. It's going to be a hell of a fight."
Photo Getty Images. Caption: Andy Ruiz Jr floors Anthony Joshua