The Conservative Party must regain voters' trust if it is to win the next election, David Cameron says.
Mr Cameron urged Conservatives to 'change to win'
The shadow education secretary launched his leadership bid by promising to campaign on "positive" issues, not some of the "negative" ones of the past.
His "core" principles included lower taxes, "national sovereignty" and a wider choice of public services.
He said: "Personal responsibility must not mean selfish individualism. There's a 'we' in politics, as well as 'me'."
The party had to welcome some of Tony Blair's policies, such as tuition fees, foundation hospitals and city academies, as they were right for the country.
Mr Cameron said Conservatism had to be "compassionate", urging: "Go for someone who believes it to the core of their being. Change to win. Change to win and we will win."
Promote national sovereignty
More choice of public services
Openness to new ideas, such as flat taxes
Broader outlook on foreign policy
Helping the weak in society
He added: "The choice for the party has got to be who do you think really believes it?
"Who will really stick to it when the going gets tough and the press attack you after a couple of years and say this is not distinctive enough, it isn't attacking enough?"
It would be "pathetic" to wait for the Labour Party to move to the left before presenting a strong alternative message.
The party had to look at new ideas, including flat income tax rates, as pioneered in eastern Europe.
Mr Cameron said: "The problem at the last election was not that people trusted the Labour Party. They didn't.
"The problem was that people don't yet trust the Conservative Party and it is we who have got to change.
"What we have to do is make a change in the culture and identity of the Conservative Party and explain what this means today."
The "proceeds of growth" in the economy had to be shared between "better public services on the one hand and lower taxes on the other hand".
Meanwhile, Mr Cameron said, national pride had to avoid "xenophobia" or "isolation".
He also restated his opposition to joining the euro.
Foreign policy had to show Conservatives were "ethically and enthusiastically" part of the wider world.
Mr Cameron said: "And when the Conservative Party talks about foreign affairs it can't just be Gibraltar and Zimbabwe.
"We have go to show as much passion about Darfur and the millions of people living on less than a dollar a day in sub-Saharan African who are getting poorer while we are getting richer."
Nominations for the leadership contest open on 10 October - after the party's conference in Blackpool - with the first round of voting among MPs taking place on Tuesday 18 October.
One candidate will drop out after each round and there will be votes every Thursday and Tuesday until two candidates remain.
There will then be a vote of the 300,000 Conservative Party members across the country to decide which of the two succeeds Michael Howard as leader.
Kenneth Clarke, Sir Malcolm Rifkind, Liam Fox and David Davis have also launched bids.