The Tory leader in Scotland called on her party to stop “hectoring the people we need to vote for us”, as she helped launch a new centrist think tank.
Ms Davidson did not mention the prime minister directly, but she said: “Sometimes as Tories we just look a bit dour. We look a bit joyless, a bit authoritarian sometimes.
“We don’t get to win if we start hectoring the people we need to vote for us. We don’t get to say ‘just stand on the right’ like every tube message out there.
“We’ve got to learn to be a bit more joyful and that’s something that we have tried to learn in Scotland. When you do it with a smile, they actually get behind you.”
The launch of the Onward think tank – designed to find fresh ideas for a Conservative Party its founders view as being in an intellectual slump – comes ahead of Ms Davidson meeting Ms May in Downing Street.
She is credited with pioneering a warmer, more exciting brand of Conservatism north of the border that many Tories would like to replicate in England.
Tipped as a future Tory leader, Ms Davidson grinned as she began her speech, telling her audience: “I’m going to create news now.”
And, after recently announcing her pregnancy, she joked she had only been invited to speak to highlight diversity within the party, saying: “Just call for the pregnant lesbian!”
Michael Gove, the environment secretary, also spoke at the launch, and echoed Ms Davidson’s call for the Tories to be more positive.
He called on his colleagues to channel musician Pharrell Williams, saying: “What we Conservatives need to do, is to remember we need to be happy.”
Mr Gove added: “The critical thing about Conservatives, as Ruth has said, is that sometimes in the past we have seemed censorious and finger-wagging, pessimistic and unhappy, uncomfortable that we seem to be living in the 21st century when the 1950s would be far more attractive and what a pity that the 19th century isn’t an option.”
Onward is the brainchild of Conservative MP Neil O’Brien, a former aide to George Osborne, and Will Tanner, Ms May’s former deputy policy chief.
It is expected to focus on how to achieve sustainable wage growth, new tech industries, devolution and better social integration, to try to attract black and ethnic minority voters.
Onward is not explicitly aligned to the Conservatives, but is being funded by Martyn Rose, an entrepreneur who used to lead David Cameron’s National Citizen Service.
Mr O’Brien has denied that the group’s name was inspired by the En Marche! (Forward) group that propelled Emmanuel Macron to power in France.