The coin has been tossed and speaking orders decided as Prime Minister Malcolm Turnbull and Opposition Leader Bill Shorten prepare to go head-to-head in the first national, free-to-air leaders' debate tonight.

Mr Shorten won the toss and chose to go second (ensuring he will get the last word in) and told reporters today he was looking forward to contrasting his party's priorities with the Coalition's.

"I'm really looking forward to discussing the difference in my priorities and my united Labor team's priorities with those of Mr Turnbull and his Liberal team," he said.

Mr Turnbull said tonight's debate would be a "good discussion" and noted there were "big issues" at stake.

"A big choice for Australia, a choice between optimism and opportunity and growth, more opportunities for all Australians, for our children and our grandchildren, the growth and jobs that come from our economic plan pave the way for a secure future," he said.

The battle will likely centre on the issue of pre-election costings, with Mr Turnbull seeking to hammer home the Coalition's point that Labor is creating a "budget black hole" in announcing more spending measures than it is finding areas to save money.

Mr Shorten will focus on the fact his party has released more policies than the Government, and there are some areas such as health and education where the need for funding outweighs a desire for fiscal conservatism.

The theatre

A prime minister has the benefit of incumbency during an election campaign, but the moment they agree to a debate, they are held at the same level as the opposition leader.

Bill Shorten has made much of the fact he has attended dozens of town hall meetings across the country in the lead up to this campaign.

While it has likely boosted his confidence as he enters the debate, the National Press Club is a very different beast — the relaxed and informal setting of speaking to the party faithful will be replaced by a panel of senior Canberra press gallery journalists and a live national television audience.

The debate is a direct pitch to the voters of Australia and an opportunity to take the opponent to task, but it is unlikely to be an all–in brawl.

Leaders' debates in recent times have become fairly beige, with combatants taking a risk-averse approach to winning over public opinion.

One only has to look at the introduction of "The Worm" to televised debates to see those charged with controlling that instantaneous gauge of public opinion respond well to platitudes, and negatively to attacks.

Picking the moment to play the aggressor is key, and it will be only be a matter of time before each leader personalises the fight — Mr Turnbull trotting out his catchphrase of "billion-dollar Bill" and Mr Shorten characterising the Prime Minister as an out-of-touch toff.

Sorry, this video has expired In 2013, then opposition leader Tony Abbott showed some aggression.

The preparation

Both leaders would have been involved in daily preparation for weeks now, memorising the facts and figures their strategists believe can deliver blows to their opponents.

To that end, the memorising of the party lines and metaphors would now be well entrenched in their minds.

But despite the preparation, quickly developed responses to surprising comments can also sway the momentum.

Sorry, this video has expired US Democratic vice presidential candidate Lloyd Bentsen had to think on his feet in the 1988 VP debate with Republican candidate Dan Quayle.

Mr Turnbull will have to respond to criticism over the Coalition's health and education funding commitments — something Labor sees as his key weakness.

On the other hand, Mr Shorten is preparing for an onslaught on the economy, and whether Labor can be trusted to manage the national purse strings.

Everything will be choreographed, from the body language to the choice of suit and tie.

Sorry, this video has expired Sometimes the choreography can come across as being quite awkward.

The verdict

Different commentators may have very different views on who walks out of the National Press Club the winner of the debate.

For the incumbent, it is a somewhat easier prospect to convince the electorate that changing government is a risk.

For the challenger, the task is to sell a new hope.

But this early on in the campaign, it is unlikely there will be a killer blow that can be fed off of until July 2.

The hour-long debate at the National Press Club in Canberra will be broadcast on ABC News 24 at 7:30pm AEST, 7:00pm in NT and SA and 5:30pm in WA.