“It’s a nightmare for everybody involved.”

That’s how former Labour adviser Ayesha Hazarika describes TV election debates.

“The amount of prep is phenomenal,” she told Sky’s Electoral Dysfunction podcast, adding that when she was working with former leader Ed Miliband on the 2015 campaign, preparation for the TV debates took “months and months”.

Former Scottish Conservatives leader Ruth Davidson told the podcast she would get her team to “rip her to shreds” with the most “unfair” and “personal” questions imaginable to ready herself for the live broadcasts.

Tonight, the Sky News Battle For Number 10 Leaders’ Special Event will see Rishi Sunak and Sir Keir Starmer face questions from political editor Beth Rigby and members of our audience in Grimsby.

Here we look at how they might be preparing – and the main dos and don’ts.

‘It’s not really about what you say’

Body language expert and business psychologist Paul Boross has years of experience preparing politicians for TV debates in several countries outside the UK.

He says viewers’ lasting impressions are rarely based on what they say.

“People are not listening to every word you’re saying. They’re watching you to get a sense of what kind of person you are,” he says.

“The public get really tired of politicians ‘banging on’ about the same thing. In the context of this election, I’m sure if they hear the word ‘plan’ again, they’ll feel like they’re going to scream.

“People are more concerned with the impression you make. As human beings, that’s the criteria we’re judging them on – whether we like and trust them.”

When preparing for head-to-head debates, the two men’s advisers will have their personal traits vivid in their minds – and look to “polish the good” and “eradicate the bad”, he adds.

What does that mean for Rishi Sunak?

Commenting on his performance at the first live TV debate, Mr Boross says: “He kept rising to the bait. He needs to sound in control and not as tetchy.”

He adds: “He also needs to find some sincerity. At the moment he seems a bit like he doesn’t care anymore – like he’s got enough money and he could just leave the country if he wanted to.”

And for Sir Keir Starmer?

With Labour so far ahead of the Conservatives in the polls, Mr Boross says Sir Keir’s main aim should be to simply “avoid any big mistakes”.

But he adds: “He can seem a bit distant. He has to try and be less prosecutorial – and more human.”

He believes the key to displaying more “lightness” and “humanity” would be to use humour effectively.

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Sunak: I’m not blind to people being frustrated with me
A history of TV debates

Outside of these individual quirks, there are a number of basic dos and don’ts the leaders can work on to prepare for tonight’s debate, according to Mr Boross.

Do…

Use people’s names

Saying a person’s name, whether they are the interviewer or an audience member, will create a “positive psychological impact” and make the interaction feel more “personal and meaningful”, Mr Boross says.

“Hearing your own name makes you feel valued and recognised.

“Good politicians repeat the name immediately when they answer the question – so they remember it initially – then repeat it throughout the conversation.”

Another way to establish a rapport with those in the room and at home is by mirroring the questioner’s language.

“Using the same language pattern as the person who asked you the question shows you’re listening and creates a bond of trust,” Mr Boross adds.

“Really good communicators always listen to what their audience is giving them and feed back in the same form – whereas bad communicators might answer a completely different question and end up alienating them.”

Keep eye contact

Speaking on Electoral Dysfunction, Ruth Davidson recalled former Liberal Democrat leader Nick Clegg’s tactic of regularly looking straight at the camera during the 2010 TV debates.

But Mr Boross says doing this too often can “feel a bit too much”.

“Completing ignoring the interviewer in favour of the TV camera would probably backfire,” he says.

Instead, leaders should keep their eyes “constantly engaged” with the person speaking to them – and only address the viewer for opening or closing statements.

Using rehearsals to decipher where the camera is and what the TV shot will look like is also worthwhile, he adds.

Expect things to go wrong – and use humour to recover

“Things are always going to go wrong,” Mr Boross says. “So I train everyone to anticipate how things might go wrong.”

This may take the form of an unexpected question, a heckler, or a physical blunder, but both humour and self-deprecation can help “change the tone”.

“Humour can win the day, because it can prick the bubble of pomposity with a bit of humanity,” Mr Boross says.

He uses the example of Green Party leader Carla Denyer, who during the second leaders’ debate waited for Labour’s Angela Rayner and Conservative Penny Mordaunt to stop arguing, before interjecting: “That was terribly dignified, wasn’t it?”

Don’t…

Talk over others

Talking over an opponent is often viewers’ biggest criticism during political debates – so waiting for others to finish speaking is an important thing to practice, Mr Boross says.

“It really irks people because it’s disrespectful – it smacks of rudeness and it’s childish.

“Psychologically we’re all considering what we’d do in that situation, and what would irritate us. So it’s better to wait and then kill them with your line.”

Speaking out of turn also suggests a lack of confidence, he adds.

Stick to the podium

Although politicians often use podiums or lecterns to rest their notes on, Mr Boross suggests “getting away” from them as soon as practically possible.

“It hides your open body language, so subliminally people are asking what you’ve got to hide,” he says.

“Tony Blair used to always keep his hands up, which goes back to that Wild West concept of ‘I have no weapons… I have nothing to hide’.”

He adds that practicing moving to the side of the podium will not only make the leaders appear “more open and honest” it also proves they can speak fluently without notes.

Physical positioning is likely to be more important for Mr Sunak, Mr Boross says, whose smaller height means more of him is hidden by the podium.

Forget facial expressions

Rehearsing your physical reactions, including facial expressions and body language, is just as important as your answers, according to Mr Boross.

“Your face gives away so much, that if you let it slip, you’re in big trouble,” he warns.

With both leaders sometimes lacking in sincerity, he adds, visualising the people or things that mean most to them while they speak could be a useful tactic.

“I often ask people to think about what they really care about – and talk with that thing or person in their mind’s eye – because then their whole demeanour will change.”

The Battle For Number 10 Leaders Special Event, Wednesday 12 June 7pm-10pm on Sky News – free wherever you get your news.

Freeview channel 233, Sky 501, Virgin 603, BT 313 and streaming on the Sky News website, app and across social channels. It is also available to watch on Sky Showcase.