Sir Menzies Campbell has said the Lib Dems have "all to play for", as he marks his first year as party leader.
His leadership has been criticised since he succeeded Charles Kennedy, but he said he had unified the party and now he was ready to step up a gear.
Arriving at his party's spring conference, he said he had pressed the government on issues like Iraq.
He said the Tories had "no substance" while Gordon Brown faced opposition from senior Labour figures.
As activists gather in Harrogate for the spring conference, which will focus on crime, Sir Menzies dismissed criticism of his early performances in the House of Commons.
"Let's put prime minister's questions into its proper context, it's not the b-all and end-all of politics in this country, it's theatre.
"Everyone wants to do better at prime minister's questions, even the prime minister, or Mr Cameron for that matter."
But he said he had been able to press the prime minister on issues like the decision to drop a fraud probe into a BAE deal with the Saudis, and on the Iraq war.
Tory leader David Cameron had had to avoid them because his party had been left "wholly compromised", due to the fact they had voted with the government on Iraq.
He accused the Conservatives of being a "policy free party" with "absolutely no substance at all".
And he said Mr Brown would "almost certainly" become the next prime minister and have to "shore up" his party, yet people who had served in the Cabinet with him were "desperate" to find an alternative to him.
"There's everything to play for for the Liberal Democrats and that's what I will be saying this weekend," he told the BBC.
Sir Menzies said he had succeeded in "steadying the ship" after a turbulent period for the party and now he was ready to step up a gear.
He said the party had been looking at issues like tax reform, environmental issues, poverty, health and education, which he said were "in despair".
Asked about speculation that they might have to go into coalition with Labour after the next general election, he said: "Let me be clear, you cannot campaign for a hung parliament."
He said he wanted the maximum number of votes and seats and was "deeply sceptical" about the statistical possibility of a hung parliament.
Despite one by-election victory in Dunfermline and East Fyfe, and a close call in another in south London, some have questioned whether Sir Menzies, aged 65, was the right man for the job.
But he told the BBC: "That kind of attack, really it suggests that when you've reached a certain age you no longer have anything to contribute in this society of ours and yet we know there are people who now work long after what used to be normal retiring age," he said.
"I think it's insulting and if I was black, female or gay people wouldn't make those points."
He has dismissed rumours he might face a leadership challenge, saying there was "no dissent" in the party's ranks.
The most highly charged debate at this weekend's conference is likely to be on whether to replace Britain's Trident nuclear weapons system.
The party leadership has said it is confident of seeing off a challenge to its policy of halving the number of warheads currently held, but putting off a decision to replace Trident until 2014.
Many grassroots activists favour unilateral disarmament but Sir Menzies has insisted such a move would damage Britain's bargaining power in persuading others to give up nuclear weapons.