Writing in The Guardian, he said: "When I first ran a general election campaign in 2001, my main focus was the election air war of posters and press conferences. The job description has changed.
"The air war still has its place but it is on the ground where this election will be won or lost. Anyone who, like me, spent last summer in church halls and village halls, high streets and doorsteps across Scotland will understand this demand for dialogue.
"The Tories may be able to outspend us by as much as three to one, but on the ground, in the key seats, we aim to outnumber their diminished and demoralised activists by the same margin as we fight this election conversation by conversation."
He said Labour’s campaign will be built around five pledges, the first two of which - covering the deficit and curbing immigration - are areas where the Tories are traditionally strong. The other three will focus on the NHS, living standards and the future for young people.
Labour leader Ed Miliband is set to criticise the Conservatives' health plans during a rally in Manchester on Monday (5 January), which the party is billing as the opening shot of its election campaign.
According to The Guardian, the Conservatives have raised £78m for their campaign over the past four years, having spent £31.1m in the 2010 general election campaign. Labour spent £8m ahead of the last general election, with the Liberal Democrats spending £4.8m.
Alexander wrote: "Our task will not be easy, not least because there are unprecedented levels of mistrust in politicians and politics itself. So the case we present on doorsteps will be concrete, clear and credible. We have already published two of our election pledges on building a strong economic foundation by balancing the books and controlling immigration in a fair way.
"Over the coming weeks you will see more, including on issues such as the NHS, our public services and the future of our young people."
On Friday the Conservative Party launched its first poster campaign for the general election, with the straPline: "Let's stay on the road to a stronger economy". It cites various achievements of the coalition Government including halving the deficit, although some claims were criticised as being misleading.