Lib Dems have been encouraged to criticise their Tory coalition partners as well as the Labour opposition.
In a leaked internal memo, senior Lib Dems were urged to spread the message that the Conservatives cannot be trusted to help build a fairer society.
Deputy Prime Minister Nick Clegg had told his party it keeps the coalition "anchored in the centre ground".
But the memo suggests voters should be reminded that the Tories wanted to "look after the super rich".
The memo from the party's head office to its MPs, peers and staff encourages them to criticise not just the Labour opposition but their Conservative coalition partners in the year ahead.
In his official new year message published on Friday, Mr Clegg said: "We are living through fluid, difficult times.
"What I can tell you is that, whatever 2013 throws at us, the Liberal Democrats will continue to anchor this coalition in the centre ground and we will hold firm to our key purpose in this government."
But the memo from a senior Lib Dem strategist uses less diplomatic language.
It tells the party's politicians that the key message for 2013 should be this - that only the Lib Dems can build a strong economy and a fairer society.
But it also suggests voters should be reminded that without Lib Dems in government, "no one could stop the Tories from looking after the super rich while ignoring the needs of normal people."
The memo then goes on to outline a series of Conservative measures which it says the Lib Dems have blocked, including "allowing bosses to fire staff at will".
It also provides Lib Dems with ammunition to fire at Labour leaders over their handling of the economy, saying: "In power they cared more about bankers, media bosses and union barons than they did about ordinary, working people."
A Lib Dem spokesman said that the memo was in line with Nick Clegg's speech at this year's party conference, when he was critical of the two other main parties.
The spokesman added that, now that the coalition is seen to be stable, both the junior and senior partners could be more frank about their differences.
The memo sets out what the Lib Dems have brought to coalition, too - including their successful demand to take more low paid workers out of tax.
But some Lib Dem activists have objected to it - not because it criticises the Conservatives, but because it also suggests that the party's representatives should make it their new year resolution to remain "on message" and "to communicate from this script at every opportunity".
At one level this could be said to demonstrate the growing professionalism of a party of government rather than of protest.
But some of the rank and file believe that too much central control over what to say and how to say it will alienate voters - and diminish the Lib Dems' ability to sound more like ordinary people than politicians.
Writing in The Liberator LibDem activist Simon Titley says the memo reveals "much what is wrong with the way the Liberal Democrats are being run".
He adds: "What we have here is an object lesson in how politics has been hollowed out and reduced to a matter of managerialism and public relations.
"It seems no-one at the top of the party has any intellectual grasp of the gravity of the situation."
The memo highlights the difficulty for the party nationally to carve a distinctive identity as a junior partner in coalition.
Where the top of the party and its grassroots are united is in feeling that the Lib Dems are getting blamed for the difficult decisions on cutting the deficit while their more positive contribution is overlooked by voters.
The party's candidate came eighth with just 2% of the vote in last month's Rotherham by election - down from a 16% showing in the same seat at the general election - and its MPs recently heard a sobering presentation on their future prospects from the new chief of staff Ryan Coetzee, who cut his teeth in post-apartheid South African politics.
So in the run-up to the 2015 election, while senior Lib Dems see no prospect of the coalition coming to an early end, there will be more openness about the negotiations they have with the Conservatives.
Insiders say their relationship will then appear to be even more businesslike, rather than pretending there is a meeting of minds. The two parties will unveil a 'mid-term' review of coalition progress early in the New Year.