Running a majority Tory government means ministers are "pulling in the same direction" rather setting up "fiefdoms" as happened under the coalition, David Cameron said.
The Prime Minister said having "one person at the steering wheel" meant the administration had a clearer sense of purpose.
He acknowledged that at times during the power-sharing deal with the Liberal Democrats ministers had to "make it up as they go along" but now they were guided by "the good book" - the Tory election manifesto.
Reflecting on the first few months of his second term, the Prime Minister highlighted the cross-government work done by Cabinet Office ministers Oliver Letwin and Matt Hancock to ensure that the new administration was working effectively.
Mr Cameron said: "I think the first 80 days have shown a Government that has got a very clear direction and purpose about delivering for working people, about building a genuinely one nation country of opportunity and also demonstrating that Britain is back on the world stage with a growing economy, a falling deficit, meeting our pledges on both defence and aid, and able to stand up for British values and British interests around the world.
"And I don't think we've wasted a day, frankly, in the last 80 days.
"I'm very pleased about the Budget and the National Living Wage.
"I think that's a really important reform, pleased that we've made progress on things like child care and reforming schools, because that is going to be vital to building opportunity, and pleased that we've been able to make steps on the international stage as well, which is in Britain's interests because we are a trading power, an international power, an engaged power."
During the coalition years, major decisions were taken by the "quad" of senior ministers - Mr Cameron, Chancellor George Osborne and the Lib Dems Nick Clegg and Danny Alexander.
Setting out how things had changed, Mr Cameron said: "In terms of doing things differently, obviously I think it does help when we've got one person at the steering wheel driving in consistently the same direction.
"It also has helped being able to bring departments together into these implementation taskforces instead of having fiefdoms perhaps run by a different party, you have got one party really working as a team so when it comes to things like improving our performance on immigration, you've got everyone, the Home Office, the education department, the Treasury, all pulling in the same direction, so I think this cross-departmental working that's going on - and I think the role particularly people like Oliver Letwin and Matt Hancock are playing - there's a great sense of teamwork across the Government and people all know if they're not sure which approach to take it's all in the good book, the manifesto, rather than having to make it up as they go along.
"So I'm happy with the progress in the last 80 days but I'm very keen we deliver all the things in our manifesto. So a lot of hard work ahead."
Despite saying he is "pumped up" and "fired up" about the task in hand, Mr Cameron insisted he would not go back on his decision not to seek a third term in Number 10.
"I've got enthusiasm for this job and I've five years ahead of me to stay on with it," he said. "Five years ahead of me, working hard at this job, I think that will be enough."