In a rousing speech on the last day of his party's conference, the Shadow Home Secretary also called on Tories to be "more normal".
It was a pitch that saw the former Cabinet minister close in on frontrunner Robert Jenrick, according to bookmakers who said Kemi Badenoch is now third in the contest with Tom Tugendhat in fourth place.
Mr Cleverly, 55, told party members that after running a small business he knew what it was like "to stumble, to fall, but to get up again and again and again".
"So when I talk about optimism, it's not just believing tomorrow can be better than today, it's doing something about it," he added.
The MP for Braintree, Essex, talked to the conference in Birmingham about his "political hero" - former US President Ronald Reagan, who he said had continued to be "upbeat" even in the depths of the Cold War.
Mr Cleverly added: "He made Americans want to vote for a conservative not reluctantly, but with enthusiasm.
"And what did he do? He cut taxes, cut regulation and boosted military spending. And he won a landslide.
"Let's be more like Reagan. Let's be enthusiastic, relatable, positive, optimistic. Let's be more normal.
"Let's sell the benefits of a Conservative government with a smile "Because if we do, we can see off the threat from Reform and the Lib Dems and win back Labour voters."
Ruling out any deals with Reform UK, Mr Cleverly insisted the best way for the Tories to keep Nigel Farage at bay was by "being the best version of ourselves".
Leadership rival Mr Jenrick told members he wanted to build a "new Conservative Party" that would end illegal migration once and for all.
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