The Eastleigh by-election showed the Lib Dems could gain seats despite being implicated in unpopular government policies, former leader Lord Ashdown told the party's spring conference in Brighton.
Ashdown said the next election would be the first the Lib Dems would fight as a party of government, meaning it would be able to campaign on its achievements.
"The message of Eastleigh is very clear - and we know it very well. Where we work, we win," Ashdown told an adoring audience.
"I'm sure that you, like me, have often told children and grandchildren that it's not the winning that matters, it's the taking part. Well let me let you into a little secret. That's bollocks."
Ashdown, who is the party's general election coordinator, said the party's core message going into the election would concern its commitment to "build a stronger economy in a fairer society, enabling everyone to get on in life".
He said the Lib Dems had gained 11 seats in local election by-elections since September, and lost none.
"After 70 years in opposition and less than three in government, one thing is clearer to me than ever. Winning matters. In opposition we can talk about our historic mission. Only in government, can we deliver on it."
Ashdown said the party would be able to show that it had already taken steps to build a stronger economy in a fairer society.
Activists would be able to combine a local message of achievement with a national message of achievement.
"That's what we did in Eastleigh. It's one of the reasons we won in Eastleigh - telling people again and again about our local and our national achievements. And it's what we have to do in our leaflets and on the doorstep this coming May, in the elections next year and in the build up to the General Election beyond."
Deputy prime minister Nick Clegg was meanwhile facing a policy revolt by Vince Cable, the business secretary, who set out his opposition to further departmental spending cuts.
Cable said political disagreements over future spending plans were so intense that this year's planned coalition spending review, due to cover 2015-16, might not be completed.
"If you keep going back to the same departments taking more than proportional cuts, you do disproportionate damage," Cable said.
Cable challenged the premise of the spending review, and Cameron's insistence that the schools, health, aid and defence equipment budgets must be excluded from the cuts, as they have been since 2010.
The decision has prompted a series of revolts at the Ministry of Defence, the Home Office and the business department.
Cable said: "All our departments should be doing their bit by efficiency and reform. We have done very brave things in the first spending round, but we have now got to the point where further significant cuts will do enormous damage to the things that really do matter like science, skills, innovation and universities."
Activists were expected to vote on plans to allow grassroots members to force a leadership contest, making it easier for the party to get rid of Clegg. The deputy prime minister also came under pressure to reveal "who knew what when" in relation to both to the Chris Huhne speeding affair, and the sexual harassment claims against party peer Lord Rennard.