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."