The rival heavyweight has been in close contact with Joshua in the build-up to the fight in Diriyah as his fellow Londoner bids to win back his WBA, IBF, WBO and IBO titles following a shock defeat to the American-Mexican in New York in June.
Chisora said: “I told Anthony just do what you do best, keep it long, make the fight boring and then take him out in the later rounds.
"Don’t mix it up with him because you know he’s got fast hands.”
Joshua had been in the ascendancy in what was his debut in America, flooring Ruiz Jr in round three, but his rival then dropped the Brit in the same round before the referee stopped the fight when the defending champion was twice floored in the seventh round.
And Chisora told talkSPORT: “Don’t worry about losing the first fight, the most important thing is the comeback, people forget your loss.”