The youngest contender in the Tory leadership race, David Cameron, has vowed to "inspire a new generation".
Speaking without notes at the Conservative conference in Blackpool the 38-year-old Mr Cameron said he wanted to end Tory election failures.
He wanted people to "feel good about being Conservatives again... I want to switch on a whole new generation".
Rival contender Ken Clarke stressed he would be straight talking and avoid political spin when he spoke later.
Mr Cameron received a three minute ovation from party representatives after his speech.
Mr Cameron said the Conservatives had to change to win back power but he warned against a move to the right, which he said would turn the party into a "fringe group".
CV: David Cameron, 38, shadow education secretary
Key Quote: "I want to switch on a whole new generation to the Conservative Party"
Best joke: "It's not just about having a young, vigorous, energetic leader - although come to think of it, it's not such a bad idea."
Ovations: 20 rounds of applause (though some of them when he thanked others) and a three minute standing ovation finale
Speech length: 19 minutes, 55 seconds
Name drops: Praise for ex-leaders Hague, Duncan Smith and Howard
Nick Assinder's verdict: Young moderniser might have swung some votes
He also warned against relying on Gordon Brown being more left wing than Tony Blair to help the Conservatives regain the centre ground, saying: "I don't want to sit around to wait and lose again in four years."
He branded Mr Brown a "great road block" in the way of public service reform and said he also stood in the way of cutting red tape and the complex tax system.
"There is only one group of people who can stop Gordon Brown - those here in this room. Let's give Gordon Brown the fright of his life," Mr Cameron told representatives.
Mr Cameron said he wanted a Conservative party "that has the courage to renew and change" - and he vowed to fight for "modern, compassionate Conservatism".
He said voters knew the Tories had failed at successive elections. "I don't want to let them down again, do you?", he asked representatives.
Ex-chancellor Mr Clarke later set out why he believes he is best placed to take on Tony Blair and Gordon Brown, pointing to his record as a tax cutting chancellor.
Many party activists in Blackpool want a "dream ticket" leadership team comprising Mr Clarke and Mr Cameron which, they believe, could unite the party.
That has been ruled out by the men themselves.
Mr Clarke told BBC News Mr Cameron was a "star of the future" who "could be a very formidable prime ministerial candidate in a few years' time".
"I am a prime ministerial candidate now."
He added: "Any sane member of the Conservative Party would want David Cameron very much on board in a Conservative shadow cabinet because he is... a very formidable intellect who can do a lot of good for this country."
Leadership rival and Eurosceptic Liam Fox has suggested the party should consider the option of withdrawing from the EU if the cost of staying in was deemed too high.
Mr Clarke said the Tories would "take ourselves into the political wilderness if we just keep banging on with the rather more extreme positions over" Europe.