Andy Ruiz is one of three men to ever beat Anthony Joshua in the ring ... and he was kind enough to share some solid advice with Jake Paul ahead of his December 19 bout!!

Ruiz (35-2, 22 KOs) handed Joshua his first career loss in 2019, with a TKO in the 7th round of their main event at Madison Square Garden in New York City -- one of boxing's biggest upsets ever. Getty

That said, we asked Ruiz -- who was distributing turkeys at the New Village Girls Academy Turkey Drive in Los Angeles this week -- if there were any suggestions he'd like to leave for the YouTuber-turned-boxer.

"Just get him with the right hand," Ruiz said, "That's what Jake Paul is lookin' for, the right hand, and if he lands, he can do good damage."

He also advises Paul to enter the ring "fearless" and not

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