George Osborne has promised "a Budget that tackles the economy's problems head-on, helping those who want to work hard and get on".
His pledge came in the Chancellor's first message on Twitter, issued on the morning of a Budget day taking place against a grim economic backdrop, with Labour pressing him to admit his austerity programme has failed.
Mr Osborne is expected to offer help to hard-pressed families by speeding up progress towards a £10,000 tax-free personal allowance.
Expectations are high that he will delay or even scrap a fuel duty hike scheduled for the autumn and abolish the so-called beer tax escalator. But the financial package is set to be dominated by questions of how to revive the ailing economy, with the Office for Budget Responsibility (OBR) likely to downgrade growth forecasts and predict sharply higher borrowing.
Mr Osborne has already signalled that a fresh round of cuts will be imposed on some Whitehall departments over the next two years to free up £2.5 billion for extra spending on housing and other infrastructure.
However, senior Liberal Democrats have been urging around £15 billion of investment funded by more borrowing.
"What I want to hear from the Chancellor today is a willingness to change course, not more of the same," said Mr Miliband. "His economic plan is failing. It's failing Britain's businesses and Britain's families."
Families are seeing their living standards fall year-on-year, while the Chancellor has given a tax break to the rich which comes into effect in less than a fortnight, said the Labour leader.
"The Government is borrowing over £200 billion more than he had planned," added Mr Miliband. "Why? Because it's paying for failure. Its failure to get growth moving. And it's also making Britain's families pay for that failure. We need a change of course from George Osborne today. What we don't need is him saying I'm going to stick to my failed plan."