Neville took the reins at Mestalla on December 2 in what is his first managerial role, following the resignation of Nuno Espirito Santo from the Liga club.
Ferguson, who managed Neville at United throughout his entire playing career at club level, told of the advice he gave during a personal visit from his former captain.
"I spoke to him; he came over to my house. And I said 'be yourself, trust your conviction, like you've done throughout your playing career and it has never let you down'. And I think that will help him," Ferguson said at the TechCrunch Disrupt London event.
Neville signed a contract with Valencia until the end of this season and watched from the stands during their 1-1 draw with Barcelona on Saturday.
He takes charge for the first time against Lyon in the Champions League on Wednesday, with the Spanish outfit needing a win to progress to the knockout stages while hoping that Gent fail to beat Zenit St Petersburg in the other match in Group H.
The 40-year-old will combine his duties with his England coaching role under Roy Hodgson and, while Ferguson believes Neville has taken a leap of faith in accepting the job, the former United manager is confident that he has the characteristics to succeed in Spain.
"Typical Gary, that he has got the courage to do something like this. It's a big step for him from owning Salford City to managing Valencia," he added.
"But he has got the football experience and he has got the role with England which will help him too.
"But the most important thing he has got is an incredible determination about him and he is a good decision-maker. He is prepared to make a decision. He has that positive attitude and he is a winner, an absolute winner, and I think he will do well."
