Senators have six year terms, so a regular election - such as this one - means only half of the Senate is up for re-election. You can find a list of the senators whose terms have expired here.

A seat that was last won on 60 per cent or more of the two-party-preferred vote is considered "safe" by the Australian Electoral Commission.

Between 56 to 60 per cent is "fairly safe" and under 56 per cent is "marginal". You will also hear election commentators talk excitedly of "ultra marginals," which are seats held on less than one per cent.

The most marginal seat in the country is the northern Queensland seat of Herbert, held by Labor on just 0.02 per cent, but hotly contested by the Liberal National Party.

The safest seat is the newly created regional Victorian seat of Nicholls, held by the Nationals on 22.6 per cent.

Due to a redistribution of electoral boundaries - to account for population changes - the number of House of Representatives seats has grown by one.

Victoria and the ACT each picked up an extra seat while South Australia lost a seat. Boundaries have also been redrawn everywhere else except Western Australia.

Because of redistributions, the seat count between the Coalition and Labor has actually changed on paper.

After the 2016 election, the Coalition had 76 seats in the lower house, and Labor had 69. After the redistribution, the Coalition went to 74 seats in the new 151 member house and Labor went up to 72.

Given various byelections and defections, the government now as 73 seats, Labor has 72 and the crossbench has six.

To have a majority on the floor of the House, plus provide a Speaker, 77 seats are needed.

The Age and The Sydney Morning Herald-Ispsos poll has had Labor ahead in every survey taken since the 2016 election. But as politicians like to remind us, the "only poll that matters is on election day".

The general election will also tease out different issues and contests, depending on the region and even the electorate.

There will be plenty of attention given to Queensland where there are five seats held on a margin of one per cent or less, and many other seats in play.

This includes Home Affairs Minister Peter Dutton's Brisbane seat of Dickson, held on 1.7 per cent.

The Townsville-based seat of Herbert is one that the Coalition is hopeful of winning back from Labor and where the battle is expected to be fierce.

The Brisbane seat of Ryan (held by the LNP on a margin of 9 per cent) could see an upset for the LNP.

In NSW, Labor is considered a strong chance of picking up Robertson on the Central Coast (held by the Coalition on 1.1 per cent), Gilmore on the South Coast (0.7 per cent) and Reid in western Sydney (4.7 per cent).

The Liberals think they have a shot at taking Lindsay off Labor (held on 1.1 per cent and where sitting MP Emma Husar is not recontesting in controversial circumstances) and there is also talk about the Central Coast seat of Dobell (4.8 per cent).

But the headline contests will be in Sydney's Warringah where Tony Abbott is being challenged by independent Zali Steggall, and Wentworth, where there will be a rematch between independent Kerryn Phelps and Liberal candidate Dave Sharma.

Liberals have been particularly nervous about Victoria after a disastrous showing for the party in the 2018 state election.

Coalition MPs feeling the pressure include frontbencher Sarah Henderson whose marginal seat of Corangamite is now nominally a Labor seat (on 0.03 per cent), thanks to a redistribution.

Former Liberal MP-turned- independent Julia Banks will challenge Health Minister Greg Hunt in Flinders and Treasurer Josh Frydenberg faces challenges from the Greens and independent Oliver Yates in Kooyong.

Outside of Melbourne, there will be interest in Indi. With Cathy McGowan retiring and lesser known local Helen Haines seeking to take her place as the local independent, the Nationals see an opportunity.

In South Australia, the Adelaide seat of Boothby is the main game for Labor, where Liberal MP Nicolle Flint has a margin of just 2.7 per cent.

In Mayo, Liberal candidate Georgina Downer is having another crack at the seat her father Alexander once held. Centre Alliance's Rebekha Sharkie is the sitting member and will have other ideas.

The last-minute retirement of Defence Minister Christopher Pyne in Sturt makes this inner-metropolitan seat, held by the Liberals on 5.4 per cent, much more interesting.

In Western Australia, minister and first lower house Indigenous MP Ken Wyatt is in trouble in Hasluck, which he holds on 2.1 per cent.

Labor is also seen as a chance to pick up Attorney-General Christian Porter's seat of Pearce (3.6 per cent), retiring frontbencher Michael Keenan's seat of Stirling (6.1 per cent), high-profile conservative Andrew Hastie's seat of Canning (6.8 per cent) and backbencher Steve Irons' seat of Swan (3.6 per cent).

In Tasmania, Labor and independent Andrew Wilkie currently hold all five of the state's lower house seats but there can be no complacency for the ALP here.

The Liberal Party is seen as a chance in Bass (5.4 per cent), Braddon (1.7 per cent) and Lyons (3.8 per cent).

A poll of more than 2000 people by the Australia Institute in March suggested Labor and the Greens would come out of the election with as many as 38 upper house seats.

This would be enough to block legislation but short of the 39 votes needed to pass it. The Coalition is predicted to secure between 30 and 32 seats.

The polling also suggests One Nation is a chance to pick up extra senators in NSW, Queensland and Western Australia.

In Tasmania, independent Jacqui Lambie may get another ticket to the Senate where Tasmanian independent, fisherman Craig Garland is also a chance.

In South Australia a tough fight between the Centre Alliance's Skye Kakoschke-Moore, the Greens' Sarah Hanson-Young, One Nation and the Liberal Party for the final spots is predicted.

The Coalition plans to springboard from the budget into the election campaign, so expect lots of talk about economic management, including attacks on Labor's plans to overhaul negative gearing and franking credits.

The Prime Minister's enthusiastic chat about "congestion busting" also suggests that infrastructure will figure prominently.

Labor is expected to argue its proposed tax changes will boost fairness, while campaigning on an increase to the minimum wage and talking up its action on climate change. It will also focus on its plans to cut the costs of cancer treatment.

It depends a bit on where they are. In regional Queensland, for example, amid concerns about jobs, there is strong support for the Adani mine to go ahead.

In metropolitan Brisbane, there is concern about climate change and opposition to coal-fired power.

The axing of Malcolm Turnbull and the influence of the right wing within the Liberal Party is predicted to hurt the government in inner metropolitan seats in Sydney and Melbourne, but the leadership change to Scott Morrison is also seen to be helping the LNP in Queensland.

Western Australian Liberal voters are understood to be annoyed that Julie Bishop was passed over for prime minister, while regional Nationals voters are angry about water management in the middle of a drought.

As one political analyst recently observed of the diversity of issues in play in 2019: "Every election is special but some are more special".

For Bill Shorten, it is the Lodge or bust. He has been opposition leader for more than five years now and this will be his second election as Labor leader.

If the ALP loses the election, there will be an automatic leadership ballot. Expect deputy leader Tanya Plibersek, Anthony Albanese and Chris Bowen to be putting up their hands in this scenario.

Scott Morrison's fate is slightly less clear. If the Coalition loses but the loss is close (and not as devastating as some polls have predicted) he may be able to hang on to the Liberal leadership.

He could reasonably argue he had not been in the job long. But if Morrison is strongly implicated in a Coalition loss, then Treasurer Josh Frydenberg, Peter Dutton and Tony Abbott would all have hopes to succeed him (provided they win their seats, of course).

After the Prime Minister calls an election, the Governor-General needs to issue the "writ" for the House of Representatives.

This is the authority for an election to be held and sets out the date when it will happen. The state governors issue the writs for Senate elections in each state.

The government then enters "caretaker period", which is a convention that means no major policy decisions will be made until the election is held and a new prime minister is sworn in.

The writ will specify the deadline for enrolling to vote or changing your enrolment details. And yes, voting is compulsory! If you don't, the Australian Electoral Commission will send you a 'please explain' letter and you face a $20 fine. Visit the AEC website to make sure your enrolment is up to date.

- SMH/The Age.